docs: guidance on PR change request timeliness and PR takeover

[Joibel]

Motivation

Document something that I think we already kind of do with regard to getting PRs reviewed.

This is somewhat to show we accept PR takeovers, in case someone is willing to pick up an PR but doesn't think they're allowed to.

Modifications

Add a section on Timeliness to the contributing guidelines suggesting the process for taking over a PR and ensuring credits go to the appropriate person.

Verification

docs only: Checked in github markdown.

[agilgur5]

This is somewhat to show we accept PR takeovers, in case someone is willing to pick up an PR but doesn't think they're allowed to.

suggesting the process for taking over a PR and ensuring credits go to the appropriate person.

I think this makes sense to document since we do get these questions and make these suggestions, although the tone currently reads more "rule" than "suggested process". I think the credit part is the only thing that should be a firm "rule" (and also proper copyright/attribution/courtesy/respect/OSS norm/etc).

Also would be good to mention the problem/more information needed label here as well, since it does apply to PRs and the specific case of authors not responding timely.

I can make more specific language suggestions later