Create .zenodo.json metadata file

This file and metadata should be picked up by Zenodo when creating
a DOI wit its GitHub integration.

See https://guide.esciencecenter.nl/citable_software/making_software_citable.html

Created with `cffconvert`

https://citation-file-format.github.io/

cffconvert --infile CITATION.cff --outputformat zenodo --outfile .zenodo.json