Document how to run with JupyterDesktop

[0Hughman0]

It is currently possible to get JupyterDesktop to work with Cassini, but this is not documented.

JupyterDesktop cannot be launched using project.launch() therefore the server cannot be started by the same interpreter as the project object, which is how this is explicitly provided usually.

Instead, the implementation found here facilitates the use of a CASSINI_PROJECT environment variable, that points the jupyter_cassini_server to the right module and object within that module to allow the project to be imported.

This means the PYTHONPATH would also need to be patched to include the project.py directory.

This needs to be added to the documentation.

There is an issue discussing related stuff on the JupyterLab extension side here.

[0Hughman0]

Oh and there'll need to be instructions on running project.setup_files() somehow, I guess recommend running from a terminal within JLDesktop?