Add a license for data provided by api

[GrumpyBear57]

Data that is LiveTL specific (aka data that we don't aggregate from something like YTC, and our users submit directly to us) should probably be licensed under something like https://creativecommons.org/licenses/by-nc-sa/4.0/

Aggregated content (like stuff from YTC) might require a different license, I'm not sure.