Clarify where docs fixes can be backported

The status key for branches has lists of changes that can go in, and the lists look exclusive:

feature:

• new features, bugfixes, and security fixes are accepted.

prerelease:

• feature fixes, bugfixes, and security fixes are accepted for the upcoming feature release.

bugfix:

• bugfixes and security fixes are accepted, new binaries are still released. (Also called maintenance mode or stable release)

security:

• only security fixes are accepted and no more binaries are released, but new source-only versions can be released

end-of-life:

• release cycle is frozen; no further changes can be pushed to it.

This makes it a bit awkward to backport docs changes, especially now that the lists are included in the tag descriptions.

AFAIK, docs fixes don't need RM approval in feature, prerelease and bugfix branches. (Security branches are locked so any change needs the RM in the loop.)
Is that right, @pablogsal @Yhg1s ?

Python Developer’s Guide にあるリンクされたステータスキーから始め、そのブランチの説明を、記載されている docs-backport に関する質問と比較してください。feature、prerelease、bugfix、security ブランチでのドキュメント修正に関する承認ルールを、該当する maintainer に確認してください。完了とは、ドキュメントの変更をどこへ backport できるのか、また RM の承認が必要かどうかをページに明確に記載することです。