Update README.md to follow Code for America format

Folllow guidelines at:
https://github.com/codeforamerica/howto/blob/master/Good-READMEs.md
Example: https://github.com/Code-for-Miami/LeafletTransit

Choose a license:
https://github.com/blog/1530-choosing-an-open-source-license

Mark as 'easy' since creating an outline of the format is good enough and the content can be filled in later - using 'todo' text is fine.
