After the joy of dealing with
https://github.com/jgrapht/jgrapht/pull/1008, I figured it is time we finally add a code of conduct to the project, which is considered best practice for open source projects these days. In the case above, I ended up locking the PR conversation, but did not ban the contributor or delete anything. However, I want to be prepared for future cases where we do end up having to ban someone for serious offenses, and having a code of conduct published is important for that.
Github has a way to add a code of conduct from a template (and also a way to block people from a project), so I've gone ahead and done that, resulting in this pull request:
Feel free to comment on that PR if there are changes you'd like to propose. The language is mostly boilerplate from the Contributor Covenant.