Recommendation for branch name testing - add CircleCI or update documentation

[cjcolvar]

CircleCI can be used to prevent the recreation of the old default branch name. This helps preserve automatic redirection to the new default branch, and prevents accidentally re-adding the legacy branch from a stale fork. If CircleCI is not integrated with this repository, please do the following:

• Add information to the README explicitly defining branch naming conventions accepted for this repository (instructions in this GitHub gist).

• Optionally, integrate CircleCI with your repository (see GitHub documentation from CircleCI), and add a test to fail when a branch called master is present (instructions in this GitHub gist).

Rationale

Git's default "master" branch derives from "master/slave" jargon which perpetuates systemic racist language and systems (see email Replacing "master" reference in git branch names). To uphold our Code of Conduct, we must move away from the term "master" in our technical language (as well as words like blacklist or whitelist).

Related work

• Background on the renaming effort is available in the working group notes.
• See the GitHub Renaming documentation for the changes that GitHub made during the renaming process.