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 ?

Start with the linked status key in the Python Developer’s Guide and compare its branch descriptions with the stated docs-backport question. Confirm the approval rules for documentation fixes on feature, prerelease, bugfix, and security branches with the relevant maintainers; done means the page clearly states where docs changes can be backported and whether RM approval is required.