Added MOOC: openSAP (#3444)

* Added MOOC: openSAP

* Update free-programming-books.md

free-programming-books.md

@@ -580,6 +580,7 @@
 * [MIT OCW](http://ocw.mit.edu)
 * [NPTEL](https://onlinecourses.nptel.ac.in)
 * [openHPI](https://open.hpi.de)
+* [openSAP](https://open.sap.com)
 * [Platzi](https://courses.platzi.com)
 * [Udacity](https://www.udacity.com)