Improve Observer Javadoc

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

@@ -6,8 +6,17 @@
 
 /**
  * 
- * Observer pattern defines one-to-many relationship between objects. The target
- * object sends change notifications to its registered observers.
+ * The Observer pattern is a software design pattern in which an object, called 
+ * the subject, maintains a list of its dependents, called observers, and notifies 
+ * them automatically of any state changes, usually by calling one of their methods. 
+ * It is mainly used to implement distributed event handling systems. The Observer 
+ * pattern is also a key part in the familiar model–view–controller (MVC) architectural 
+ * pattern. The Observer pattern is implemented in numerous programming libraries and 
+ * systems, including almost all GUI toolkits.
+ * <p>
+ * In this example {@link Weather} has a state that can be observed. The {@link Orcs}
+ * and {@link Hobbits} register as observers and receive notifications when the
+ * {@link Weather} changes.
  * 
  */
 public class App {