updating exercise 4 description

Author: samuil4

EXERCISE/Exercise 4/readme.md

@@ -17,3 +17,21 @@
   * must have template
   * must have a destroy method
   * event system
+
+# The actual task
+
+* web app representing an OS desktop
+* create and destroy windows from the controller
+* each window must have:
+  * title
+  * content
+  * close button - destroys the window
+  * minimize button - minimizes the window
+  * maximize button - maximazes the application
+  * representation in the bottom sidebar
+  * template to be rendered with
+  * unique ID
+ * public method exit - destroys all windows
+ * public method clean - minimizes active window
+ * only one window must be shown at a time
+ * create your own style and markup