Refine release process / cadence

[hunterowens]

Currently, ReleaseGuidlines.md dictates the main release process for MDS. Notably, it doesn't commit to any particular release timeline, and only really address "how" to make a release once it is ready, not "what makes a release candidate".

It is also unclear who exactly will be reviewing any given PRs, and given the constraints on my time, PRs / issues don't get the attention and/or care they deserve.

There are number of issues that a refined release process could help, and moving to both a regular schedule and defined comment period could really help.

Additionally, we have no CONTRIBUTING.md, although there is a proposed one in #170. We should make it clear on how to contribute and what will happen once you make a PR or Issue, or would like to comment outside of github.

I'd like to do a number of things to improve the release process will help with the questions raised in #206.

[jfh01]

Proposal for CONTRIBUTING.md is in #176 as well.

[hunterowens]

With #264 merged, closing this for now.