github: customize pull request template for documentation

[tmorrell]

:heart: Thank you for your contribution!

Description

This customizes the pull request template to match the new branch names. Should not be merged until new branches are in place.

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• [x] I'm aware of the code of conduct.
• [x] I've created logical separate commits and followed the commit message format.

Reminder

By using GitHub, you have already agreed to the GitHub’s Terms of Service including that:

1. You license your contribution under the same terms as the current repository’s license.
2. You agree that you have the right to license your contribution under the current repository’s license.

[fenekku]

Ok merging since it's not a blocker (as in merging when Nico is good :wink: )