Update notebooks in advance of publication

Author: wesm

README.md

@@ -2,7 +2,8 @@
 
 Materials and IPython notebooks for "Python for Data Analysis, 3rd
 Edition" by Wes McKinney, published by O'Reilly Media. Book content
-can be [found for free on my website][6].
+including updates and errata fixes can be [found for free on my
+website][6].
 
 [Buy the book on Amazon][1]