Contributor guide is out of date or not enforced #72

The contributor's guide for this repository is out of date and should be updated, or the recommendations there should be enforced. For example, the develop branch is out of date, and we're not following the gitflow recommendation of pull requests submitted to develop. Personally, I don't mind master being the tip as long as fixes can be backported to version branches.

If using a develop branch is important for this project, then I think the develop branch should be set as the default branch in GitHub and GH Actions should be used to enforce these processes: https://help.github.com/en/github/administering-a-repository/defining-the-mergeability-of-pull-requests

There should also be an update to the section on managing the changelog when this lands: #68