Add a topic on jupyter-lmod in documentation

[cmd-ntrf]

This is a first draft of new topic for Lmod's documentation and address issue #639.

Comments and thoughts are welcomed.

[lexming]

Looks good, I only have a few minor comments. Please see below

[lexming]

Maybe add a link to your repo from the start 🙂

Suggested change

	It is possible to use Lmod inside of Jupyter with the terminal or jupyter-lmod.
	It is possible to use Lmod inside of Jupyter with its terminal or the Jupyter extension `jupyter-lmod <https://github.com/cmd-ntrf/jupyter-lmod>`_.

[lexming]

This sentence is a bit confusing, I suggest to simplify it:

Suggested change

	jupyter-lmod uses lmod python interface to generate Python code
	that modifies the environment variables of the Python process running Jupyter. All child
	processes of Jupyter (including kernels) created after Lmod calls inherit
	the environment variables as defined by the set of loaded modules.
	jupyter-lmod uses lmod python interface to generate Python code
	that modifies the environment variables of the Python process running Jupyter. All child
	processes of Jupyter (*e.g.* newly spawned kernels) will inherit the environment
	as currently defined by the set of loaded modules.

[lexming]

Technically these variable are only needed in the single-user server. JupyterHub itself does not need them.

Suggested change

	If the environment variables are defined before JupyterHub launch, you can add their
	names only to `c.Spawner.env_keep <https://jupyterhub.readthedocs.io/en/stable/api/spawner.html#jupyterhub.spawner.Spawner.env_keep>`_
	instead.
	If the environment variables are already defined before JupyterHub is launched
	or before the single-user server starts (Jupyter Notebook or JupyterLab),
	you can propagate these variable by adding their names to
	`c.Spawner.env_keep <https://jupyterhub.readthedocs.io/en/stable/api/spawner.html#jupyterhub.spawner.Spawner.env_keep>`_ instead.