Add License section

Author: donnemartin

README.md

@@ -1745,3 +1745,9 @@ Special thanks to:
 Feel free to contact me to discuss any issues, questions, or comments.
 
 My contact info can be found on my [GitHub page](https://github.com/donnemartin).
+
+## License
+
+    Creative Commons Attribution 4.0 International License (CC BY 4.0)
+
+    http://creativecommons.org/licenses/by/4.0/