Put an empty `__init__.py` file in the rfcatomni/openomn directory

[yeagerm]

Need to put an empty __init__.py file in the rfcatomni/openomni directory so that it is properly recognized as a python package directory. Useful for virtual python environments like Virualenv and Anaconda distributions. Can use: pip install -e . rather than pip install -e . --process-dependency-links as outlined in the installation instructions for the RFCAT https://github.com/openaps/openomni/tree/master/rfcatomni

http://python-notes.curiousefficiency.org/en/latest/python_concepts/import_traps.html#the-missing-init-py-trap

[Lytrix]

Good catch, Thanks for the PR! I've changed the readme.