doc: Provide developer documentation for preparing releases

[langston-barrett]

We should have some docs on how we prepare releases for this project. For example:

• Who (if anyone) is the point-of-contact for this process?
• Do we generally cut a branch for each major release, and backport fixes for further minor releases?
• What is our version numbering scheme? (This is especially important to document given that it involves some non-standard business with .99, see here for some commentary.)
• Should we upgrade and test downstream projects before cutting a release? If so, which ones?
• What are some things to look out for when reviewing release prep? (For example, perhaps one should run cabal check and ensure there are no new warnings.)
• How do we announce releases?
• and so on...

@sauclovian-g mentioned there was some ongoing (or upcoming?) work that might be relevant here.

[sauclovian-g]

Yeah, there is. The short answer is that we more or less need to release everything at once and that makes it all a gigantic production. I'll try to make sure you're in the loop updating such process docs as we have.