Add documentation about flake8+hacking.

- Fixes bug 1201431.

Change-Id: If025a41caf3a629b9efb4d67c53c423796d37a91

doc/source/development_guidelines.rst

@@ -51,6 +51,24 @@ To execute the unit tests:
 
   - `tox -e pep8,py26`
 
+------------
+Coding Style
+------------
+
+Swift use flake8 with the OpenStack `hacking`_ module to enforce
+coding style.
+
+Install flake8 and hacking with pip or by the packages of your
+Operating System.
+
+It is advised to integrate flake8+hacking with your editor to get it
+automated and not get `caught` by Jenkins.
+
+For example for Vim the `syntastic`_ plugin can do this for you.
+
+.. _`hacking`: https://pypi.python.org/pypi/hacking
+.. _`syntastic`: https://github.com/scrooloose/syntastic
+
 ------------------------
 Documentation Guidelines
 ------------------------