Merge pull request #34 from antoviaque/install-requirements-pre

Install steps - Add numpy requirement in manual installation steps

README.md

@@ -76,6 +76,7 @@ environment), and Node has a library installer called
 Once you've got your languages and virtual environments set up, install
 the libraries like so:
 
+    $ pip install -r requirements/edx/pre.txt
     $ pip install -r requirements/edx/base.txt
     $ pip install -r requirements/edx/post.txt
     $ bundle install