Add Whirlwind Tour link

jakevdp · jakevdp · commit b68389f02681 · 2016-08-15T09:49:16.000-07:00
diff --git a/README.md b/README.md
@@ -5,6 +5,8 @@ Supplemental materials for my OReilly project, the
 
 ![cover image](cover-early-release.jpg)
 
+See also the free companion project, [A Whirlwind Tour of Python](https://github.com/jakevdp/WhirlwindTourOfPython).
+
 
 ## Code Listings
 
