adding chapter 4 Stacks

Author: crizstian

README.md

@@ -9,7 +9,8 @@ The purpose of this repo is to update the exercises to ES6 standards.
 
 ## Examples covers
 
-| **Num** | **Type** |
+| **Num** | **Type** | **Excercises** |
 --- | ---
-| 1.- | Array |
-| 2.- | Lists |
+| 1.- | Array | 4 |
+| 2.- | Lists | 5 |
+| 3.- | Stacks | 3 |