docs: clarify patch release changelog

[endorama]

Clarify how to create PR to provide documentation for patch releases.

[mergify]

This pull request does not have a backport label. Could you fix it @endorama? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.

NOTE: backport-skip has been added to this pull request.

[endorama]

Skip backport is fine as is a docs change.