Add pip specific content contribution rosdep rules for Gentoo (#29909)

* Add pip specific content for Gentoo
Fixes: #29908

Co-authored-by: Chris Lalancette <[email protected]>

.github/pull_request_template.md

@@ -25,7 +25,8 @@ Distro packaging links:
 
 ## Links to Distribution Packages
 
-<!-- Replace the REQUIRED areas and state not available for IF AVAILABLE -->
+<!-- Replace the REQUIRED areas with the URL to the package.  For IF AVAILABLE areas, either put in the URL to the package or state 'not available'.
+More info at https://github.com/ros/rosdistro/blob/master/CONTRIBUTING.md#guidelines-for-rosdep-rules -->
 
 - Debian: https://packages.debian.org/
   - REQUIRED

CONTRIBUTING.md

@@ -136,6 +136,9 @@ TODO
 If the ebuild you are referencing is not in either of those locations, please
 file a PR into ROS-Overlay to add it and any needed dependencies to the tree.
 
+Note that `pip` cannot be used to install system packages on Gentoo.
+If the package is not present in the Gentoo package repository, please create an issue on the https://github.com/ros/ros-overlay repository so that it may be created at a later date, omit the key from the new rosdep rule, and link the created issue in the PR which is adding the rule. [Here's a simple example](https://github.com/ros/ros-overlay/issues/1019).
+
 #### Arch Linux
 
 Packages must be in the official Archlinux core, extra, or community repositories at the time they are contributed.
@@ -228,6 +231,9 @@ Some existing rules do not have `python-` or `python3-` prefixes, but this is no
 If the package ever becomes available in Debian or Ubuntu, the `python3-` prefix ensures that the `pip` key is next to it alphabetically.
 The `-pip` key should be removed when the package becomes available on all platforms, and all existing users of the `-pip` key should migrate to the new key.
 
+As a reminder `pip` rules should not be used on Gentoo.
+See above for the Gentoo specific guidelines.
+
 How to submit pull requests
 ---------------------------