add link to CS 228 ipython version of tutorial

Author: jcjohnson

python-numpy-tutorial.md

@@ -35,6 +35,8 @@ computing.
 
 Some of you may have previous knowledge in Matlab, in which case we also recommend the [numpy for Matlab users](http://wiki.scipy.org/NumPy_for_Matlab_Users) page.
 
+You can also find an [IPython notebook version of this tutorial here](https://github.com/kuleshov/cs228-material/blob/master/tutorials/python/cs228-python-tutorial.ipynb) created by [Volodymyr Kuleshov](http://web.stanford.edu/~kuleshov/) and [Isaac Caswell](https://symsys.stanford.edu/viewing/symsysaffiliate/21335) for [CS 228](http://cs.stanford.edu/~ermon/cs228/index.html).
+
 Table of contents:
 
 - [Python](#python)