Add license

[henryreed]

Hello!

Awesome work! Really love this repo.

I was wondering if you could add a license to allow for code reuse? Personally I am a fan of Creative Commons Zero v1.0 Universal, since it's equivalent to waiving copyright in countries where it's legal and, where it's not, it falls back to a "public domain equivalent license."

Let me know if you have any questions! Looking forward to your response.