Adding short book on Computational Thinking to Free Programming Books (#3955)

* Adding short book on Computational Thinking to Free Programming Books

* Adding a short book/document about computational thinking

free-programming-books.md

@@ -399,6 +399,7 @@
 
 #### Computer Science
 
+* [Computational Thinking](https://www.cs.cmu.edu/~15110-s13/Wing06-ct.pdf) - Jeannette Wing, Carnegie-Mellon University (PDF)
 * [Computer Science I - Draft](https://bitbucket.org/chrisbourke/computersciencei/src) - Dr. Chris Bourke (PDF) (:construction: *in process*)
 * [Computer Science II - Draft](http://cse.unl.edu/~cbourke/ComputerScienceTwo.pdf) - Dr. Chris Bourke (PDF) (:construction: *in process*)