setup.py solidpython dependencies

[T-Wainwright]

Currently the setup.py file doesn't install solidpython, meaning the code does not work out the box for someone running windio2cad for the first time. Additionally instructions for a user not using conda for package manager would be useful:

sudo apt-get update 
sudo apt-get openscad
python3.8 -m venv windio2cad
source windio2cad/bin/activate
pip install -e .