add readme, cover

Author: amueller

README.md

@@ -1,2 +1,18 @@
-# introduction_to_ml_with_python
-Notebooks and code for the book "Introduction to Machine Learning with Python"
+# 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.
+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
+0.18-dev.  Most of the book can also be used with previous versions of
+scikit-learn, though you need to adjust the import for everything from the
+``model_selection`` module, mostly ``cross_val_score``, ``train_test_split``
+and ``GridSearchCV``.
+
+This repository provides the notebooks from which the book is created, together
+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)