Document the the release process

[jhkennedy]

Should include:

• [ ] mechanics of releasing (how to do it)
• [ ] the release workflow (what happens)
• [ ] potential issues and how to fix them (what to do if something goes wrong)

[dbekaert]

@jhkennedy I assume this can be closed if we move part of the text you had in the PR into the README #416 ? I guess the what happens if something goes wrong is missing.

[jhkennedy]

@dbekaert I've been meaning to write something up that's a little more comprehensive than that, so I'll do that sometime this week. And we can then either point to it in the README or CONTRIBUTING, or add it to a docs/release_proccess.md file.