Update README.rst to include config files and updated interpreters.

Author: Nurdok

README.rst

@@ -20,7 +20,7 @@ Use `pip <http://pip-installer.org>`_ or easy_install::
 Alternatively, you can use ``pep257.py`` source file
 directly--it is self-contained.
 
-**pep257** is tested with Python 2.6, 2.7, 3.2, 3.3
+**pep257** is tested with Python 2.6, 2.7, 3.2, 3.3, 3.4, pypy and pypy3.
 
 Example
 -----------------------------------------------------------
@@ -130,3 +130,27 @@ are grouped as follows:
 +--------------+--------------------------------------------------------------+
 | D402         | First line should not be the function's "signature".         |
 +--------------+--------------------------------------------------------------+
+
+Configuration
+-----------------------------------------------------------
+``pep257`` looks for a config file in the root of the project (the common
+prefix of all checked files) and goes up in the directory tree until it finds
+one of the following files (in this order):
+
+* ``setup.cfg``
+* ``tox.ini``
+* ``.pep257``
+
+The first found file is read, and configurations in the ``[pep257]`` section
+are used, if such a section exists.
+
+Config Example
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code::
+
+    [pep257]
+    verbose = true
+    ignore = D100,D203,D405
+    explain = true
+