Python: Update README with information about code formatting

Also, add a `yapf` section to `setup.cfg` to ensure YAPF runs
format code with the Google style.

python/README.md

@@ -1,5 +1,38 @@
-This directory contains Python brotli wrapper module and roundtrip tests.
+This directory contains the code for the Python `brotli` module,
+`bro.py` tool, and roundtrip tests.
 
-To build module execute `python setup.py build_ext` from root project directory.
 
-To test module run `python setup.py test`.
+### Development
+
+To build the module, execute the following from the root project
+directory:
+
+    $ python setup.py build_ext
+
+To test the module, execute the following from the root project
+directory:
+
+    $ python setup.py test
+
+
+### Code Style
+
+Brotli's code follows the [Google Python Style Guide][].  To
+automatically format your code, install [YAPF][]:
+
+    $ pip install yapf
+
+Then, either format a single file:
+
+    $ yapf --in-place FILE
+
+Or, format all files in a directory:
+
+    $ yapf --in-place --recursive DIR
+
+See the [YAPF usage][] documentation for more information.
+
+
+[Google Python Style Guide]: https://google.github.io/styleguide/pyguide.html
+[YAPF]: https://github.com/google/yapf
+[YAPF usage]: https://github.com/google/yapf#usage