add links to author websites

Author: amueller

README.md

@@ -1,7 +1,7 @@
 # Introduction to Machine Learning with Python
 
 This repository holds the code for the forthcomming book "Introduction to Machine
-Learning with Python" by Andreas Mueller and Sarah Guido.
+Learning with Python" by [Andreas Mueller](http://amueller.io) and [Sarah Guido](https://twitter.com/sarah_guido).
 You can find details about the book on the [O'Reilly website](http://shop.oreilly.com/product/0636920030515.do>).
 
 The books requires the current development version of scikit-learn, that is
@@ -15,4 +15,5 @@ with the ``mglearn`` library of helper functions to create figures and
 datasets.
 
 For the curious ones, the cover depicts a [hellbender](https://en.wikipedia.org/wiki/Hellbender)
+
 ![cover](cover.jpg)