Create LICENSE

[macdonst]

We really need to create a LICENSE file. From codinghorror:

Because I did not explicitly indicate a license, I declared an implicit copyright without explaining how others could use my code. Since the code is unlicensed, I could theoretically assert copyright at any time and demand that people stop using my code. Experienced developers won't touch unlicensed code because they have no legal right to use it.

We want to explicitly signal that folks are free to use and experiment with this repo.