citations file

[keewis]

• [x] follow-up to #80

This adds a CITATION.cff file, together with a pre-commit hook that validates it. Note that this is an initial draft, so feel free to suggest changes.

[tinaok]

@keewis here are 2 orcid missing;

@benbovy : https://orcid.org/0009-0001-4011-3574 @danlooo :0000-0002-4024-4443