Add a license and contributing guidelines

[inputsh]

By not licensing your list, you're kind of copyrighting it.

You’ll have to check with your own legal counsel regarding your particular project, but generally speaking, the absence of a license means that default copyright laws apply.

Also, short CONTRIBUTING.md file would be nice.

These are steps that we're kind of trying to enforce in all of the awesome lists to make the contributing process easy and accessible to anyone.