Add license to README.

Just want to kick off a travis build :)

Author: Ethan Cohen

README.md

@@ -50,6 +50,10 @@ Then configure the rules you want to use under the rules section.
 - no-access-key: Enforce that the accessKey prop is not used on any element to avoid complications with keyboard commands used by a screenreader.
 - use-label-for: Enforce that label elements have the htmlFor attribute
 
+## License
+
+MIT License.
+