Missing dependency: make docs

It seems like there is a missing dependency declaration in the setup.cfg to build the docs. On a fresh minterpy installation, one gets:

$ pip install -e .[docs]
...
$ cd docs/
$ make html
Running Sphinx v4.3.2
making output directory... done
...
Notebook error:
NoSuchKernel in getting-started/one-dimensional-function-interpolation.ipynb:
No such kernel named python3
make: *** [html] Error 2

The issue is resolved if one installs jupyter via

$ pip install jupyter

I think we should add this dependency (or a smaller one which also resolves the issue) to the [options.extras_require] in setup.cfg.