Updated readme to with info on assets license, including link to not-yet-existing vcmi-assets repository

README.md

@@ -15,6 +15,7 @@ For building from source see project wiki at http://wiki.vcmi.eu/
 
 ## Copyright and license
 
-VCMI Project is released under GPL version 2 or later
+VCMI Project source code is licensed under GPL version 2 or later.
+VCMI Project assets are licensed under CC-BY-SA 4.0. Assets sources and information about contributors are available under following link: [https://github.com/vcmi/vcmi-assets]
 
 Copyright (C) 2007-2014  VCMI Team (check AUTHORS file for the contributors list)