Docs (Setup) : Add instructions about virtual environment to Dioptra Setup

[colton-lapp]

The "prepare the deployment" instructions specify to install Cruft in a virtual environment for the pre-requisites section. I think this is a little easy to miss, and ideally there would be more thorough instructions about setting up a virtual environment.

I've personally always been confused if there should be a separate virtual environment in each deployment folder, and one in the dioptra root directory... or if you can use the one from the dioptra root directory everywhere. In either case, we should include some syntax for how to install dependencies in the pyproject TOML file. An explanation that distinguishes the two directories, when you need to be in each, and what their virtual environments are used for would be helpufl.