Add Licensing statement to README file (#353)

README.md

@@ -18,3 +18,7 @@ As a piece of software in its Alpha cycle, the code is continuously changing and
 - Web service API endpoints that allow third party applications to work with the datasets
 - Integration with a decoupled [REACT front end](https://github.com/getdkan/data-catalog-frontend) 
 - A datastore to store CSV files and make them queryable through an SQL endpoint.
+
+## License
+
+DKAN and related modules are freely-available under the ["GNU General Public License, version 2 or any later version"](https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html) license.