Use CITATION.cff instead of CITATION.bib

I am reviewing the CITATION usage in the repos and in particular moving to CFF files. The bib can still be generated using Github menu.
Here are a couple of suggestions to adapt this repo:

- [ ] use CITATION.cff instead of CITATION.bib ; a good example is https://github.com/JuliaSmoothOptimizers/CaNNOLeS.jl/blob/main/CITATION.cff and/or you can use this tool https://citation-file-format.github.io/cff-initializer-javascript/#/
- [ ] update the link in the README.md after that

Review the existing CITATION.bib and README.md, using the linked CaNNOLeS.jl example and CFF initializer as references. Replace the citation file with CITATION.cff and update the README.md link; the work is done when the repository uses CFF and the README points to it.

Written by the indexing model from the issue text.