Merge pull request #208 from ericguirbal/mooc

Add MOOC edX

free-programming-books.md

@@ -317,6 +317,7 @@
 * [MIT OCW](http://ocw.mit.edu/OcwWeb/web/home/home/index.htm)
 * [Coursera](https://www.coursera.org/)
 * [Udacity](https://www.udacity.com/)
+* [edX](https://www.edx.org/)
 
 ####Professional Development
 * [Don't Just Roll the Dice](http://download.red-gate.com/ebooks/DJRTD_eBook.pdf) (PDF) *(RedGate, By Neil Davidson)*