Run flake8 in Travis CI. Add note to README

Change-Id: I5257af7d20dc396e7f65d769aa2eb4a534b824fa

ci/travis_script_python.sh

@@ -92,7 +92,10 @@ python_version_tests() {
   conda install -y -q nomkl
 
   # Expensive dependencies install from Continuum package repo
-  conda install -y -q pip numpy pandas cython
+  conda install -y -q pip numpy pandas cython flake8
+
+  # Fail fast on style checks
+  flake8 pyarrow
 
   # Build C++ libraries
   rebuild_arrow_libraries

python/README.md

@@ -38,7 +38,20 @@ On Linux, you can also install binary wheels from PyPI with pip:
 pip install pyarrow
 ```
 
-### Development details
+## Development
+
+### Coding Style
+
+We follow a similar PEP8-like coding style to the [pandas project][3].
+
+The code must pass `flake8` (available from pip or conda) or it will fail the
+build. Check for style errors before submitting your pull request with:
+
+```
+flake8 pyarrow
+```
+
+### Building from Source
 
 See the [Development][2] page in the documentation.
 
@@ -50,4 +63,5 @@ python setup.py build_sphinx -s doc/source
 ```
 
 [1]: https://github.com/apache/parquet-cpp
-[2]: https://github.com/apache/arrow/blob/master/python/doc/source/development.rst
+[2]: https://github.com/apache/arrow/blob/master/python/doc/source/development.rst
+[3]: https://github.com/pandas-dev/pandas