Added explanation about class adapter vs. object adapter in the adapter

example.

adapter/src/main/java/com/iluwatar/App.java

@@ -2,8 +2,14 @@ package com.iluwatar;
 
 /**
  * 
- * Adapter (GnomeEngineer) converts the interface of the
- * target class (GoblinGlider) into suitable one expected
+ * There are two variations of the Adapter pattern: The
+ * class adapter implements the adaptee's interface whereas
+ * the object adapter uses composition to contain the adaptee
+ * in the adapter object. This example uses the object adapter
+ * approach.
+ * 
+ * The Adapter (GnomeEngineer) converts the interface of the
+ * target class (GoblinGlider) into a suitable one expected
  * by the client (GnomeEngineeringManager).
  *
  */