Added LICENSE based on README.md

[applejag]

Hi! Having the license stored in a file named LICENSE is convention throughout open source.

Automated tooling for extracting licenses, such as license-check, have a hard time when the license is only cited in the README.md.

This PR adds the same license text as that from the README.md, but wrapped to not go beyond 80 characters (which is the conventional formatting of licenses/raw text documents).