Create script to generate jupedsim.org website locally

[Ozaq]

We rely on GH-Actions right now to generate the website content however when updating the documentation it is sometimes handy to be able to quickly build everything locally. The process is not very complicated and boils (almost) down to:

pip install -r docs/requirements
pip install . sphinx-build -T -b html docs/source docs/build -j

# optionally exclude notebooks
nb_execution_excludepatterns = [] # insert pattern to exclude all or specific notebooks

This should be packed into a nice (probably python) cli tool.