Update README.md

[dzyphr]

Use python3 -m pip install -r requirements.txt instead of pip3 install -r requirements to make sure we are installing the requirements into the active virtual environment and not just the user's outer installation of python.

[bitschmidty]

Sounds good to me although Im not a pythonista

[dzyphr]

In my experience the libraries will not load for the workshop unless it is installed this way.