fix typo

Author: samuil4

EXERCISE/Exercise 4/readme.md

@@ -2,7 +2,7 @@
 
 ## Features
 
-* Create a singlton (app) structure to control the application - controller
+* Create a singelton (app) structure to control the application - controller
   * method init - called on window load
   * public methods
     * setter methods
@@ -16,4 +16,4 @@
   * must have a constructor
   * must have template
   * must have a destroy method
-  * event system
+  * event system