docs: guide to installables docs in installable commands' docs

The installables syntax is not documented in any of the man pages or
docbook pages for any of those individual commands. And while these
commands really should at least peripherally individually document how
installables work, in the meantime we can at least direct people to the
right place.

This commit also clarifies the unexpected fact that `nix profile remove`
and `nix profile upgrade` do *not* take installables.

Change-Id: I3b1453cb197a613bbab639c66a466365c3592c6d

21 files changed, 41 insertions, 1 deletions

diff --git a/src/nix/build.md b/src/nix/build.md
index 0fbb39cc3..2435c1ef6 100644
--- a/src/nix/build.md
+++ b/src/nix/build.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Build the default package from the flake in the current directory:
diff --git a/src/nix/bundle.md b/src/nix/bundle.md
index 89458aaaa..156f040ba 100644
--- a/src/nix/bundle.md
+++ b/src/nix/bundle.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Bundle Hello:
diff --git a/src/nix/derivation-add.md b/src/nix/derivation-add.md
index f116681ab..ba75b402a 100644
--- a/src/nix/derivation-add.md
+++ b/src/nix/derivation-add.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Description
 
 This command reads from standard input a JSON representation of a
diff --git a/src/nix/derivation-show.md b/src/nix/derivation-show.md
index 1296e2885..f644a429d 100644
--- a/src/nix/derivation-show.md
+++ b/src/nix/derivation-show.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Show the [store derivation] that results from evaluating the Hello
diff --git a/src/nix/develop.md b/src/nix/develop.md
index c49b39669..e39048bb1 100644
--- a/src/nix/develop.md
+++ b/src/nix/develop.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Start a shell with the build environment of the default package of
diff --git a/src/nix/diff-closures.md b/src/nix/diff-closures.md
index 0294c0d8d..5f81aa4e2 100644
--- a/src/nix/diff-closures.md
+++ b/src/nix/diff-closures.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Show what got added and removed between two versions of the NixOS
diff --git a/src/nix/edit.md b/src/nix/edit.md
index 89bd09abf..d120f3205 100644
--- a/src/nix/edit.md
+++ b/src/nix/edit.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Open the Nix expression of the GNU Hello package:
diff --git a/src/nix/eval.md b/src/nix/eval.md
index d1daaf755..eb9f753c5 100644
--- a/src/nix/eval.md
+++ b/src/nix/eval.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Evaluate a Nix expression given on the command line:
diff --git a/src/nix/fmt.md b/src/nix/fmt.md
index 1c78bb36f..8b90f33ef 100644
--- a/src/nix/fmt.md
+++ b/src/nix/fmt.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 With [nixpkgs-fmt](https://github.com/nix-community/nixpkgs-fmt):
diff --git a/src/nix/log.md b/src/nix/log.md
index 01e9801df..81bfefd96 100644
--- a/src/nix/log.md
+++ b/src/nix/log.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Get the build log of GNU Hello:
diff --git a/src/nix/nix.md b/src/nix/nix.md
index e0f459d6b..7a4a03395 100644
--- a/src/nix/nix.md
+++ b/src/nix/nix.md
@@ -162,7 +162,7 @@ The Nix expression in that file, or any selected attribute, must evaluate to a d
 
 Example: `--expr 'import <nixpkgs> {}' hello`
 
-When the option `--expr` *expression* \[*attrpath*...\] is given, installables are interpreted as the value of the of the Nix expression.
+When the option `-E` / `--expr` *expression* \[*attrpath*...\] is given, installables are interpreted as the value of the of the Nix expression.
 If attribute paths are provided, commands will operate on the corresponding values accessible at these paths.
 The Nix expression, or any selected attribute, must evaluate to a derivation.
 
diff --git a/src/nix/path-info.md b/src/nix/path-info.md
index 2dda866d0..5f31215d7 100644
--- a/src/nix/path-info.md
+++ b/src/nix/path-info.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Print the store path produced by `nixpkgs#hello`:
diff --git a/src/nix/print-dev-env.md b/src/nix/print-dev-env.md
index a8ce9d36a..a7b1cc2b6 100644
--- a/src/nix/print-dev-env.md
+++ b/src/nix/print-dev-env.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Apply the build environment of GNU hello to the current shell:
diff --git a/src/nix/profile-install.md b/src/nix/profile-install.md
index 4c0f82c09..8fe31ac4d 100644
--- a/src/nix/profile-install.md
+++ b/src/nix/profile-install.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Install a package from Nixpkgs:
diff --git a/src/nix/profile-remove.md b/src/nix/profile-remove.md
index ba85441d8..91684b9eb 100644
--- a/src/nix/profile-remove.md
+++ b/src/nix/profile-remove.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note**: unlike [`nix profile install`](./nix3-profile-install.md), this command does *not* take installables.
+
 # Examples
 
 * Remove a package by position:
diff --git a/src/nix/profile-upgrade.md b/src/nix/profile-upgrade.md
index 39cca428b..b24ab8e3d 100644
--- a/src/nix/profile-upgrade.md
+++ b/src/nix/profile-upgrade.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note**: unlike [`nix profile install`](./nix3-profile-install.md), this command does *not* take installables.
+
 # Examples
 
 * Upgrade all packages that were installed using an unlocked flake
diff --git a/src/nix/repl.md b/src/nix/repl.md
index c5113be61..f8ad49199 100644
--- a/src/nix/repl.md
+++ b/src/nix/repl.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Display all special commands within the REPL:
diff --git a/src/nix/run.md b/src/nix/run.md
index 250ea65aa..7639e4d3e 100644
--- a/src/nix/run.md
+++ b/src/nix/run.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Run the default app from the `blender-bin` flake:
diff --git a/src/nix/search.md b/src/nix/search.md
index f65ac9b17..c0e48d4b3 100644
--- a/src/nix/search.md
+++ b/src/nix/search.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Show all packages in the `nixpkgs` flake:
diff --git a/src/nix/shell.md b/src/nix/shell.md
index f36919575..598a39854 100644
--- a/src/nix/shell.md
+++ b/src/nix/shell.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Start a shell providing `youtube-dl` from the `nixpkgs` flake:
diff --git a/src/nix/why-depends.md b/src/nix/why-depends.md
index dc13619e1..fdbebbedc 100644
--- a/src/nix/why-depends.md
+++ b/src/nix/why-depends.md
@@ -1,5 +1,7 @@
 R""(
 
+**Note:** this command's interface is based heavily around [*installables*](./nix.md#installables), which you may want to read about first (`nix --help`).
+
 # Examples
 
 * Show one path through the dependency graph leading from Hello to