Added Online Python Tutor

I found this tool helpful when I started to learn how to code and I thought that this should be on the list.

Author: Sidhant Bhavnani

docs/intro/learning.rst

@@ -30,7 +30,13 @@ If you want a more traditional book, *Python For You and Me* is an excellent
 resource for learning all aspects of the language.
 
     `Python for You and Me <http://pymbook.readthedocs.org/>`_
+Online Python Tutor: a basic understanding of how your code will run
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+pythontutor.com is an easy way to get introduced to Python and programming in general.
+In Python Tutor you will see a visual step by step representation of how your program runs.
+Python Tutor helps people overcome a fundamental barrier to learning programming by understanding what happens as the computer executes each line of a program's source code.
+    `Online Python Tutor <http://pythontutor.com/>`_
 
 Invent Your Own Computer Games with Python
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~