Added doc to tell people they should use git hooks.

doc/internal/dev_start_guide.txt

@@ -102,6 +102,28 @@ typo) to keep the history clean, you can do it like this:
    git commit --amend
    git push -u origin  my_shiny_feature:my_shiny_feature
 
+
+Coding Style Auto Check
+-----------------------
+
+In Theano, we use the same coding style as the `Pylearn
+<http://deeplearning.net/software/pylearn/v2_planning/API_coding_style.html>`_
+project. The principal thing to know is that we follow the
+`pep8 <http://www.python.org/dev/peps/pep-0008/>`_ coding style.
+
+We use git hook provided in the project `pygithooks
+<https://github.com/lumberlabs/pygithooks>`_ to validate that commit
+respect pep8. This happen when each user commit, not when we
+push/merge to the Theano repository. Github don't allow us to have
+code executed when we push to the repository. So we ask all
+contributor to use those hooks.
+
+For historic reason, we currently don't have all file respecting pep8.
+We decided fix everything incrementally. So not all file respect it
+now. So we strongly suggest that you use the "increment" pygithooks
+config option to have a good workflow. See the pygithooks main page
+for how to set it up for Theano and how to enable this option.
+
 Cleaning up history
 -------------------