Feature: Add contribution instructions

[ckhatton]

I would like to add instructions on how to contribute to the project. I was going create an 'issue' to ask if this branching practice could be used from now on (or if one is being used), but I thought I would just go ahead an create it. I don't mind if the idea is rejected, as I was going to write similar instructions for my own repos.

It also details how to version number.

If you agree to accept this pull request, then please merge it to a branch named 'develop' using the --no-ff flag, which follows the new guidelines set out in CONTRIBUTE.md 😃

You could increase my level of access, so I can just do it myself 😉

[mde]

Definite plus one for adding contributing instructions. However, there is some overlap between this and the Contributing page on the wiki (https://github.com/geddy/geddy/wiki/Contributing-to-Geddy). We should probably pick one or the other, or maybe have a summary in the file, and link to the wiki for more details.

The release strategy you describe in the file is not the same as what we were previously using. There's a brief description of it in the wiki page -- basically development happens on master, and release branches for major versions (e.g., v13) are spun off of that. (Those are effectively versioned production branches.)

Bugfixes for the release branch are done against the release branch, and then cherry-picked back into master.

[mde]

The Geddy codebase is not that huge. I don't know if I'd characterize it as "excessive." Having a note about maintenance-mode might be fine, but "stale" seems a little harsh. :)