add spacy and nltk installation instructions

Author: amueller

README.md

@@ -42,7 +42,8 @@ scikit-learn.
 ## Setup
 
 To run the code, you need the packages ``numpy``, ``scipy``, ``scikit-learn``, ``matplotlib``, ``pandas`` and ``pillow``.
-Some of the visualizations of decision trees and neural networks structures also require ``graphviz``.
+Some of the visualizations of decision trees and neural networks structures also require ``graphviz``. The chapter
+on text processing also requirs ``nltk`` and ``spacy``.
 
 The easiest way to set up an environment is by installing [Anaconda](https://www.continuum.io/downloads).
 
@@ -51,6 +52,10 @@ If you already have a Python environment set up, and you are using the ``conda``
 
  conda install numpy scipy scikit-learn matplotlib pandas pillow graphviz python-graphviz
 
+For the chapter on text processing you also need to install ``nltk`` and ``spacy``:
+
+ conda install nltk spacy
+
 
 ### Installing packages with pip
 If you already have a Python environment and are using pip to install packages, you need to run
@@ -60,6 +65,14 @@ If you already have a Python environment and are using pip to install packages,
 You also need to install the graphiz C-library, which is easiest using a package manager.
 If you are using OS X and homebrew, you can ``brew install graphviz``. If you are on Ubuntu or debian, you can ``apt-get install graphviz``.
 Installing graphviz on Windows can be tricky and using conda / anaconda is recommended.
+For the chapter on text processing you also need to install ``nltk`` and ``spacy``:
+
+ pip install nltk spacy
+
+### Downloading English language model
+For the text processing chapter, you need to download the English language model for spacy using
+
+ python -m spacy download en
 
 ## Submitting Errata