DOC Clarify that this is the second edition code

Also, link to first_edition branch for readers looking for that
information.

Author: luispedro

README.md

@@ -1,11 +1,14 @@
 Building Machine Learning Systems with Python
 =============================================
 
-Source Code for the book Building Machine Learning Systems with Python by
-[Willi Richert](http://twotoreal.com) and [Luis Pedro
-Coelho](http://luispedro.org).
+Source Code for the book Building Machine Learning Systems with Python by [Luis
+Pedro Coelho](http://luispedro.org) and [Willi Richert](http://twotoreal.com).
 
-The book was published in 2013 by Packt Publishing and is available [from their
+The book was published in 2013 (second edition in 2015) by Packt Publishing and
+is available [from their
 website](http://www.packtpub.com/building-machine-learning-systems-with-python/book).
 
+The code in the repository corresponds to the second edition. Code for the
+first edition is available in [first\_edition
+branch](https://github.com/luispedro/BuildingMachineLearningSystemsWithPython/tree/first_edition).