docs: Fix build deps and Python Bindings page.
[CONTRIBUTING.md] - In order to be able to build the documentation, the package `sphinxcontrib-katex` also needs to be installed via pip. [docs/guides/python_bindings.md] - According to the matplotlib documentation , the second argument to `imshow` needs to be a string describing a colormap name or an instance of a ColorMap. An error occurred with the previously used argument as it did not describe a defined colormap. As the argument is optional, it can just be omitted (or replaced according to personal style preferences). - The relative link to the Quickstart page did not work, it has been replaced by a doc-link according to the sphinx documentation .  matplotlib.org/3.5.0/api/_as_gen/matplotlib.pyplot.imshow.html  docs.readthedocs.io/en/stable/guides/cross-referencing-with-sphinx.html#the-doc-role