Name conflicts with pip install oca

[jcdrubay]

I guess that you are already aware that package oca already exists in pypi: https://pypi.python.org/pypi/oca/4.10.0

Should we temporarily update the installation section with:

pip install git+https://github.com/LasLabs/python-oca

instead of

pip install oca

[lasley]

Good call, thanks @jcdrubay. We'll wait for OCA to take the repo in order to determine the PyPi name. Fixed in #4