Added link to the online book

Author: rougier

README.md

@@ -2,7 +2,7 @@
 
 [![Binder](http://mybinder.org/badge.svg)](http://mybinder.org:/repo/rougier/numpy-100/notebooks/100%20Numpy%20exercises.ipynb)
 
-This is a collection of numpy exercises from numpy mailing list, stack overflow, and numpy documentation. I've also created some problems myself to reach the 100 limit. The goal of this collection is to offer a quick reference for both old and new users but also to provide a set of exercises for those who teach.
+This is a collection of numpy exercises from numpy mailing list, stack overflow, and numpy documentation. I've also created some problems myself to reach the 100 limit. The goal of this collection is to offer a quick reference for both old and new users but also to provide a set of exercises for those who teach. For extended exercises, make sure to read [From Python to NumPy](http://www.labri.fr/perso/nrougier/from-python-to-numpy/).
 
 → [Test them on Binder](http://mybinder.org:/repo/rougier/numpy-100/notebooks/100_Numpy_exercises.ipynb)  
 → [Read them on GitHub](100_Numpy_exercises.md)