Document the release process

[langston-barrett]

Now that we have releases (#67), it would be great to document the process of cutting a new release so we never have malformed releases. At a minimum, this should include:

1. Moving the "Unreleased" notes in the changelog to a section titled with the new version number
2. Bumping the versions in the CLI and Cabal files
3. Copy major changes to the "What's New" section of the README
4. Create a new git tag with git tag -a "vX.Y.Z" -m "", and push with git push --tags