Update MainApp.java

Added a short explanation of the application's logic.

model-view-presenter/src/main/java/com/iluwatar/MainApp.java

@@ -1,5 +1,20 @@
 package com.iluwatar;
 
+/**
+ * 
+ * The Model-View-Presenter(MVP) architectural pattern, helps us achieve what is
+ * called "The separation of concerns" principle. This is accomplished
+ * by separating the application's logic(Model), GUIs(View), and finally 
+ * the way that the user's actions update the application's logic(Presenter).
+ * 
+ * In the following example, The FileLoader class represents the app's logic,
+ * the FileSelectorJFrame is the GUI and the FileSelectorPresenter is
+ * responsible to respond to users' actions.
+ * 
+ * Finally, please notice the wiring between the Presenter and the View
+ * and between the Presenter and the Model.
+ * 
+ */
 public class MainApp {
 
 	public static void main(String[] args) {