Add many Nix/NixOS packages. (#29070)

* Add many Nix/NixOS packages.

* Add documentation for NixOS

Co-authored-by: Jacob Perron <jacob@openrobotics.org>

.github/pull_request_template.md

@@ -41,7 +41,8 @@ Distro packaging links:
   - IF AVAILABLE
 - Alpine: https://pkgs.alpinelinux.org/packages
   - IF AVAILABLE
-
+- NixOS/nixpkgs: https://search.nixos.org/packages
+  - OPTIONAL
 
 
 <!-- DOC_INDEX_TEMPLATE: add package to rosdistro for documentation indexing -->

CONTRIBUTING.md

@@ -76,6 +76,7 @@ Guidelines for rosdep rules
     * Ubuntu and Debian are top priority.
     * Fedora and Gentoo have packaging jobs and should be filled in if they are available.
     * OSX is also nice to have.
+    * NixOS is not required, but may be added if desired
     * If specific versions are called out, there should be coverage of all versions currently targeted by supported ROS distros.
      * If there's a new distro in prerelease adding a rule for it is fine.
        However please don't target 'sid' as it's a rolling target and when the keys change our database gets out of date.
@@ -135,6 +136,11 @@ Work has been proposed to add a separate installer for AUR packages [ros-infrast
 * FreeBSD project pkg repository: main or quarterly
 * A database of FreeBSD packages is available at https://freshports.org
 
+#### NixOS/nixpkgs
+
+* [NixOS unstable channel](https://github.com/NixOS/nixpkgs/tree/nixos-unstable), search available at https://search.nixos.org/packages
+* [nix-ros-overlay](https://github.com/lopsided98/nix-ros-overlay)
+
 #### pip
 
 For pip installers they are expected to be in the main PyPI index https://pypi.org/.

rosdep/ruby.yaml

@@ -78,6 +78,7 @@ ruby:
   fedora: [ruby, ruby-devel, openssl-devel, rubygems]
   gentoo: [dev-lang/ruby]
   macports: [ruby]
+  nixos: [ruby]
   ubuntu:
     '*': [ruby]
     lucid: [ruby1.8-dev, libopenssl-ruby1.8, rubygems1.8]
@@ -105,12 +106,14 @@ ruby-dev:
   fedora: [ruby-devel, openssl-devel, rubygems]
   gentoo: [dev-lang/ruby]
   macports: [ruby]
+  nixos: [ruby]
   ubuntu: [ruby-dev]
 ruby-ronn:
   arch: [ruby-ronn]
   debian: [ruby-ronn]
   fedora: [rubygem-ronn]
   gentoo: [app-text/ronn]
+  nixos: [ronn]
   ubuntu: [ruby-ronn]
 ruby-sass:
   debian: [ruby-sass]