Update README.md

README.md

@@ -10,6 +10,8 @@ Svelto.ECS is easy to start with, but full of tricks for expert users. The harde
 ```csharp
     public class SimpleContext
     {
+        public static ExclusiveGroup group0 = new ExclusiveGroup(); //the group where the entity will be built in
+
         public SimpleContext()
         {
             var simpleSubmissionEntityViewScheduler = new SimpleEntitiesSubmissionScheduler();