Propose changes in PR process

[namcios]

Update CONTRIBUTING.md with proposed changes in the PR review/edit process by maintainers. Also added some steps in PR creation process. Did not mention PR editing by non-maintainers because I believe that applies more to translations and not all repos (will create another PR for TRANSLATING.md where applicable).

Draft proposal. Please inform me of any further changes wanted/needed.

Discussed in Community Issue #62. Probably also applies to Community Issue #30.

[namcios]

Also mentioning @shannona here for review/feedback.

[shannona]

Thanks for the updates @namcios.

For the "GPG signed commits" I'd suggest putting in a short listing (possibly as a separate doc) that actually provides the step-by-step of setting up signatures, as it's scattered here and is tricky. I think we just need:

(1) Setup a GPG signature
(2) Tell GitHub about the GPG Signature
(3) Example of how to use

[And tell people that of course they can use their own, existing signature if they want, and at that point just point them to the existing doc on how to do so for lots of different sigs. We just want to provide the steps by steps for people potentially unfamiliar with sigs at all.]

I also wonder about why we're suggesting that editors do so from the command line. I personally find it much simpler to go over PRs from the web interface, so I'm not sure why we're recommending the other as a default.

Thanks!