Add LICENSE

[allentiak]

Probably Apache 2 would be a good choice here? (It's just like EPL, but GPL-compatible.)

You may find this link interesting: https://www.datamation.com/open-source/bruce-perens-how-many-open-source-licenses-do-you-need/

And, if you have some more time, this one as well: https://dwheeler.com/essays/gpl-compatible.html