Add CITATION.cff file

[pjbriggs]

Adds a CITATION.cff to the Github repository, which will then make a "Cite this repository" option on the repository front page.

See:

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

Initial version produced using the tool at https://citation-file-format.github.io/cff-initializer-javascript/

[pjbriggs]

There are a couple of things I'm unsure of:

• How to address the "chicken-and-egg" issue of including the automatically-generated DOI created by Zenodo when it ingests a release, within the source code archive for that release
• It appears that the citation information generated from the CITATION.cff file points to the Github repository, but my understanding was that it was preferable to reference DOIs (which should be permanent) over Github repos (which may be transient)

Looking at the example within the Turing Way documentation at https://the-turing-way.netlify.app/communication/citable/citable-cff#cm-citable-cff I see that Zenodo actually generates a DOI for all archived versions (what they call the "concept" DOI, see https://zenodo.org/help/versioning).

Since the CITATION.cff format includes a top-level doi: field (see e.g. https://github.com/citation-file-format/citation-file-format/blob/main/CITATION.cff) one solution might be to use the concept DOI, however this is not recommended by Zenodo as they prefer the version-specific DOIs (see the "versioning" document linked previously). Also it's not clear if doi: overrides repository-code: (which I assume is being used when generating the reference).

There is a practical reason why this is important, as I would like to also update the citation information within the documentation (currently this also points to the Github repository).

[pjbriggs]

It's still not clear how best to populate the citation file so for now I'm going to add the version that cites the GitHub repository, and modify the citation information printed by the program and that in the documentation to match.