Add a citation file

[areleu]

It would be nice if you had this to ease up the citation of your repository, it is an extra place where one has to watch out for the version and author changes but I think it makes it a lot easier to refer to specific CCO versions in papers. If you have a CITATION.cff file GitHub even automatically formats the citation text:

https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-citation-files

You can even adjust it to your liking so it refers to a specific publication, if that is what you want people to cite.