Document release process

[pavithraes]

As the release processes are updated, we need to document the new workflow to release on PyPI and conda-forge for current and future maintainers.

(Originally noted by @ptomecek, @ngoldbaum, and @trallard)

Items to be included

• Git for maintainers
  • Make origin your fork, set upstream to the real repo, add remotes for collaborators as needed
  • How to check out a PR locally
  • Dealing with old unmerged PRs (pushing fixups to other people's forks, when to do this and when not to)
  • Setting up commit signing and adding signing keys to github
• Github for maintainers
  • Triaging issues
  • Code review guidelines and checklist
  • Communication guidelines
• Doing a "normal" release
  • Choosing a new version number
  • Generating an author list from git
  • Writing release notes
• Tagging the release and pushing to github
  • Dealing with a release mistakes
  • Yanking for completely broken releases
  • Post releases for metadata fixes (e.g. a readme fix or to fix version constraints)
  • Permanent deletion for publishing private data, but this should be avoided
  • Doing a new release with a fix

Additional items that need documenting:

• versioning approaches (SemVer)

[ngoldbaum]

This is done now.