Split nix-env and nix-store documentation per-subcommand

Documentation on "classic" commands with many sub-commands are
notoriously hard to discover due to lack of overview and anchor links.
Additionally the information on common options and environment variables
is not accessible offline in man pages, and therefore often overlooked
by readers.

With this change, each sub-command of nix-store and nix-env gets its
own page in the manual (listed in the table of contents), and each own
man page.

Also, man pages for each subcommand now (again) list common options
and environment variables. While this makes each page quite long and
some common parameters don't apply, this should still make it easier
to navigate as that additional information was not accessible on the
command line at all.

It is now possible to run 'nix-store --<subcommand> --help` to display
help pages for the given subcommand.

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>

1 files changed, 25 insertions, 0 deletions

diff --git a/doc/manual/src/command-ref/nix-store/add.md b/doc/manual/src/command-ref/nix-store/add.md
new file mode 100644
index 000000000..87d504cd3
--- /dev/null
+++ b/doc/manual/src/command-ref/nix-store/add.md
@@ -0,0 +1,25 @@
+# Name
+
+`nix-store --add` - add paths to Nix store
+
+# Synopsis
+
+`nix-store` `--add` *paths…*
+
+# Description
+
+The operation `--add` adds the specified paths to the Nix store. It
+prints the resulting paths in the Nix store on standard output.
+
+{{#include ./opt-common.md}}
+
+{{#include ../opt-common.md}}
+
+{{#include ../env-common.md}}
+
+# Example
+
+```console
+$ nix-store --add ./foo.c
+/nix/store/m7lrha58ph6rcnv109yzx1nk1cj7k7zf-foo.c
+```