Update CITATION file with current citation recommendations

[bencomp]

As identified by @efran the CITATION file currently just says FIXME. It would be good to replace that with current information, similar to other Data Carpentry repositories.

[bencomp]

Not to get in your way, but in yesterday's maintainer meeting I asked about guidelines for the CITATION file and the answer was "this needs more thought". See https://github.com/carpentries/maintainer-resources/blob/main/2022/2022-07-20.md for the notes.

It ties in with the process of creating a release of the lesson, thinking about/deciding who counts as author etc.