[GA-1532] Document how to cite geocat-applications

[cyschneck]

Add citation information and instructions (README and Table of Contents)

• Zenodo DOI
• Update README
• Update sidebar

[kafitzgerald]

We should also include a CITATION.cff file. There's more info on these from GitHub and the Turing Way has more complete description that has info on how these interact with Zotero and how to generate them. In short, there's a tool to generate the CITATION.cff file and Zenodo should pick up the metadata from the CITATION.cff file in the repo and populate the DOI metadata from that.

If I recall correctly, creating the Zenodo DOI is fairly easy, but requires admin permissions on the repo.

For GeoCAT, we may want to look at Zenodo communities as well. This would give us some additional features / permissions at a group level otherwise there's just a single account responsible for the DOI. I think we can move existing DOIs to a community as well which might be nice.

Another thing we'll probably want to think about is how we populate the metadata and recognize contributions to this project. There's some relevant discussion on the Pangeo Discourse. Unfortunately, it sounds like the all-contributors bot isn't approved on the NCAR GitHub org at this point. That's something we could look into though and/or consider following the associated specification.