Document steps for Python 2

Author: myint

README.rst

@@ -60,7 +60,11 @@ Installation
 
 To install via pip::
 
-    $ pip install --user --upgrade language-check
+    $ pip install --upgrade language-check
+
+If you are using Python 2, you'll need to install 3to2 beforehand::
+
+    $ pip install --upgrade 3to2
 
 
 Prerequisites