added support for tutorial ipynb using nbsphinx: my initial plan was
to add myST markdown notebooks, however, these do not work with binder
and colab, since nothing except notebooks in github repositories can
be used with these services
added buttons for colab and binder to the tutorial notebooks; I would
have preferred to use pyodide, however, torch does not yet work with
pyodide
added an image classification tutorial using VGG11
two new documentation requirements: nbsphinx and ipykernel
the tutorial ipython notebooks are executed when building the
documentation