DOC updated docstrings, requirements

Author: eigenfoo

README.md

@@ -10,7 +10,8 @@ A simple Rocchio-tfidf text categorizer.
 ## Installation
 
 To get `textcat` up and running, the following code snippet should suffice on a
-UNIX terminal:
+UNIX terminal (note that depending on your Python distribution, you may need to
+use `pip3` instead of `pip`, and `python3` instead of `python`):
 
 ```
 $ git clone https://github.com/eigenfoo/textcat.git

nltk_download.py

@@ -1,5 +1,8 @@
-import nltk
+'''
+Download all necessary nltk packages.
+'''
 
+import nltk
 nltk.download('stopwords')
 nltk.download('punkt')
 nltk.download('wordnet')

requirements.txt

@@ -1,2 +1,2 @@
-dill==0.2.7.1
-nltk==3.2.5
+dill>=0.2.7.1
+nltk>=3.2.5