Update README.md

I specified that most of the code has a GNU GPL v3 license, with the exception of the class.lua file, which belongs to Mathias Richter and has a special license.

Author: eduardoluis11

README.md

@@ -2,7 +2,9 @@
 
 ## License: 
 
-The code for this game is released under the GNU General Public License v3.0 (https://www.gnu.org/licenses/gpl-3.0.en.html). Meanwhile, the sprites for this game are released under the CC BY-SA 4.0 license (https://creativecommons.org/licenses/by-sa/4.0/ .)
+Most of the code for this game, with the only exception of the class.lua file, is released under the GNU General Public License v3.0 (https://www.gnu.org/licenses/gpl-3.0.en.html .) Meanwhile, the class.lua file is released with a special license. Read the class.lua file to find the full description of the license used for that file. The class.lua file is copyright of Matthias Richter. 
+
+The sprites for this game are released under the CC BY-SA 4.0 license (https://creativecommons.org/licenses/by-sa/4.0/ .)
 
 #### Video Demo:  https://youtu.be/SgNr82sFVFs