Add a citation.cff file

[drvinceknight]

Looks like Github now lets you add a citation file which creates a nice Cite this repository widget.

https://twitter.com/natfriedman/status/1420122675813441540

[drvinceknight]

Info about the citation.cff file format here: https://citation-file-format.github.io

[VartanAhrensKayayan]

I can create the citation file. But I need to know does Axelrod want to be cited? Is there a published paper you wish to refer to or a few major contributors that the code can attributed to?

[meatballs]

https://github.com/Axelrod-Python/Axelrod/blob/master/CITATION.rst

[VartanAhrensKayayan]

Ok, I created the CITATIONS.cff. See #1405.

[drvinceknight]

I've set the CI going. Thanks for your patience :)

[VartanAhrensKayayan]

The citation file has been added, maybe this should be closed?