Added usage instructions for autopep8

Author: kdelwat

docs/writing/style.rst

@@ -452,6 +452,23 @@ Then run it on a file or series of files to get a report of any violations.
     optparse.py:472:29: E221 multiple spaces before operator
     optparse.py:544:21: W601 .has_key() is deprecated, use 'in'
 
+The program `autopep8 <https://pypi.python.org/pypi/autopep8/>`_ can be used to
+automatically reformat code in the PEP 8 style. Install the program with:
+
+.. code-block:: console
+
+    $ pip install autopep8
+
+Use it to format a file in-place with:
+
+.. code-block:: console
+
+    $ autopep8 --in-place optparse.py
+
+Excluding the ``--in-place`` flag will cause the program to output the modified
+code directly to the console for review. The ``--aggressive`` flag will perform
+more substantial changes and can be applied multiple times for greater effect.
+
 Conventions
 ----------------