Add more detailed contributing information

[jaredmorgs]

Add a basic procedure about how to contribute a fix that isn't a typo.

This enhancement was identified in the slack #general room.

[mgan59]

👍 Looks good!

[flicstar]

+1 Looks good

[camerons]

I'm -0 (non blocking vote against).
I think the idea is right, but some more is required.

• We are introducing a conflict in advice further in the doc. (Update suggests notifying slack, below it suggests email list).
• Further down it talks about issue tracking, and the inserted section is also talking about issue tracking.
• In our weekly meeting one of the main issues Max identified is permissions granted to approve pull requests. I think it is worth noting that this is going to become more rigorous over time. Currently we trust of Project Steering Committee tech writers to make a call on accept/reject. But we shouldn't accept our own pull requests.

Separate to this pull request, we should consider grouping this document in the same repository as our other governance docs: E.g.: https://github.com/thegooddocsproject/governance/blob/master/ProjectSteeringCommittee.md

[jaredmorgs]

@camerons I think if we get this PR applied then we can take a closer look at the other sections of this file and clean them up a bit.

For now, lets "iterate, not gold plate" and get this contributing info in.

[jaredmorgs]

@flicstar or @camerons can you Squash and Merge if you are OK with the closing comment I made please?

[camerons]

I'm about to merge this pull request in line with Jared's suggestion of iterate rather than gold plate.