Add documentation on installing required Python modules

[JeremyMcCormick]

On ifarm at JLab, I'm using this python module:

module load python/3.9.5

I had to do this to get psutil installed and found properly:

python3 -m pip install --user psutil

This should be noted in our documentation, as just executing pip won't work in all cases. On ifarm, this will find the wrong pip from /usr/local for instance instead of the loaded Python module.

Similar deal is needed for autopep8 source code formatting:

python3 -m pip install --user autopep8