Add a license file?

[IAlibay]

It would be useful to know what this data is licensed under.

[davidlmobley]

Good idea; apparently I did this repo before making that standard practice for me. I should apply CC-BY for data that I control and MIT for code. Unfortunately the phrase "that I control" is doing a lot of heavy lifting there because the ultimate answer to this probably depends on obscure legal issues relating to whether taking data out of a table in a journal article (or taking it from someone else who did so) gives me "control" over it to apply my own license to it. IDK. Still, I should put a license on the repo.