Docs: Updates docs when the Jupyter Notebooks are modified (automatically)

[EwoutH]

Currently, when Jupyter Notebooks (.ipynb) files are updated, the documentation isn't, because it's generated from the reStructuredText (.rst) files.

In #1078, for example, intro_tutorial.ipynb is updated but intro_tutorial.rst isn't, so the Introductory Tutorial is still badly formatted.

Two potential solutions for this:

• When an Jupyter Notebook is modified, regenerate the reStructuredText (ideally automated in CI)
• Generate the docs directly from the Jupyter Notebooks (maybe using nbsphinx?)