Issue DOI for this cookbook

[brian-rose]

It's time for our first "release" and the minting of a DOI.

[brian-rose]

Struggling to get this working. Zenodo has yet to accept any of the three releases I have issued. It's showing

{
    "error_id": "09227d4dca584e6b9bdbb8dbc6461418",
    "errors": "Citation metadata load failed"
}

https://zenodo.org/account/settings/github/repository/ProjectPythia/radiative-feedback-cookbook

I haven't identified anything obviously wrong with our CITATION.cff file. It might help to run it through a validator first.