Add general description for the example code

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

@@ -38,7 +38,33 @@ import com.iluwatar.hexagonal.service.LotteryServiceImpl;
 
 /**
  * 
- * Example application demonstrating Hexagonal Architecture
+ * Hexagonal Architecture pattern decouples the application core from the
+ * services it uses. This allows the services to be plugged in and the 
+ * application will run with or without the services.<p>
+ * 
+ * The core logic, or business logic, of an application consists of the 
+ * algorithms that are essential to its purpose. They implement the use 
+ * cases that are the heart of the application. When you change them, you 
+ * change the essence of the application.<p>
+ * 
+ * The services are not essential. They can be replaced without changing 
+ * the purpose of the application. Examples: database access and other 
+ * types of storage, user interface components, e-mail and other 
+ * communication components, hardware devices.<p>
+ * 
+ * This example demonstrates Hexagonal Architecture with a lottery system.
+ * The application core is separate from the services that drive it and
+ * from the services it uses.<p>
+ * 
+ * The primary ports for the application are {@link LotteryAdministration} 
+ * through which the lottery round is initiated and run and 
+ * {@link LotteryService} that allows players to submit lottery tickets for 
+ * the draw.<p>
+ * 
+ * The secondary ports that application core uses are {@link WireTransfers}
+ * which is a banking service, {@link LotteryNotifications} that delivers
+ * notifications as lottery events occur and {@link LotteryTicketRepository}
+ * that is the storage for the lottery tickets.
  *
  */
 public class App {