Merge pull request #1547 from fredericksilva/python-tutorial

 add "Learn Python" - close #1520

free-courses-en.md

@@ -132,6 +132,7 @@
 * [Berkeley's Structure and Interpretation of Computer Programs](http://www-inst.eecs.berkeley.edu/~cs61a/)
 * [Google's Python Course](https://developers.google.com/edu/python/)
 * [Introduction to Computer Science and Programming](http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-00sc-introduction-to-computer-science-and-programming-spring-2011/) (MIT's opencourseware)
+* [Learn Python](https://pythonspot.com)
 
 ### RethinkDB
 * [RethinkDB: Distributed Databases](https://courses.platzi.com/courses/rethinkdb-databases/)