Update README.md

Author: ThijssjihT

README.md

@@ -1,4 +1,8 @@
 # Schaduwen en Kleuren
 Just open the html file in a html5 compatible browser with javascript enabled.
 
-You are allowed to do whatever you want with this code, except for taking it as is, and claiming it as your own.
+You are allowed to do whatever you want with this code, except:
+- You may not take this software without modifications, and claim it as your own.
+- Any modifications made by you must be shared on request, as long as your project is active.
+
+I chose a GPLv2 licence, and it may or may not be appropriate here.