iluwatar#467 data-bus: App: add description of the pattern

Author: kemitix

data-bus/src/main/java/com/iluwatar/databus/App.java

@@ -35,6 +35,17 @@
  * The Data Bus pattern
  * <p>
  * <p>{@see http://wiki.c2.com/?DataBusPattern}</p>
+ * <p>
+ * <p>The Data-Bus pattern provides a method where different parts of an application may
+ * pass messages between each other without needing to be aware of the other's existence.</p>
+ * <p>Similar to the {@code ObserverPattern}, members register themselves with the {@link DataBus}
+ * and may then receive each piece of data that is published to the Data-Bus. The member
+ * may react to any given message or not.</p>
+ * <p>It allows for Many-to-Many distribution of data, as there may be any number of
+ * publishers to a Data-Bus, and any number of members receiving the data. All members
+ * will receive the same data, the order each receives a given piece of data, is an
+ * implementation detail.</p>
+ * <p>Members may unsubscribe from the Data-Bus to stop receiving data.</p>
  *
  * @author Paul Campbell (pcampbell@kemitix.net)
  */