update readme

README.md

@@ -219,6 +219,16 @@ To run the tests:
     vendor/bin/phpunit -c test/phpunit.xml test/
 </pre>
 
+## License
+
+This software library is released under the [GNU GPL V3 or later license](http://www.gnu.org/copyleft/gpl.html)
+
+This software library is Copyright (c) 2015-2016, Ashley Kitson, UK
+
+A commercial license is available for this software library, please contact the author. 
+It is normally free to deserving causes, but gets you around the limitation of the GPL
+license, which does not allow unrestricted inclusion of this code in commercial works.
+
 ## History
 
 V0...  pre releases