add license file

[pz-max]

hey @GordStephen , could you add a license to this repo?
You can use GitHub or https://reuse.software/ to select the appropriate license

[GordStephen]

Thanks for pointing out that oversight... I just added the same 3-Clause BSD license we used for the original portal. This repo's really more data than software, which raises some questions about whether a software license makes sense, but I suppose this is better than nothing for now.