Create DOI for each database release

[mpinsky]

It would help if users could cite specific versions. This should be do-able with Zenodo and GitHub releases.

[mpinsky]

@df511 From the Github instructions and this page, it appears that we can get a DOI for each release made through Github, which is perfect. I was previously worried it would be one DOI for all releases.

It also sounds like the "the list of authors for the citation is automatically determined by the GitHub user account names used by the repository." It's worth checking whether this is going to include everyone in the Pinsky lab (which we don't want) or just those of us who have contributed to this repo (Michelle, Dan, Malin, which is what we want).