Add git to installation requirements

[jdpigeon]

git is necessary to install pygatt

[micuat]

we can probably use setup.py to avoid git
http://python-packaging.readthedocs.io/en/latest/dependencies.html#packages-not-on-pypi

[hubertjb]

Good point, people could just download a zip archive from https://github.com/peplin/pygatt and then use pip install . from inside the pygatt directory.

[micuat]

pointer to the section of the instruction to be revised:
https://github.com/NeuroTechX/bci-workshop/blob/master/INSTRUCTIONS.md#installation-of-additional-python-packages