Add Jupyter notebooks as demos/tutorials

[HDembinski]

The documention in the README is pretty good, but it would be even better to include Jupyter notebooks in the repository under a directory "tutorials" or "examples" which show how to make typical plots.

[eduardo-rodrigues]

Agreed. If you look at Particle, DecayLanguage and boost-histogram you will see that they all contain a notebooks directory. @andrzejnovak, how about that?

[andrzejnovak]

I agree this should be updated. Ideally into a binder along with Nicks mpl-hep gallery. It's on my long term to-do, but a PR is welcome

[HDembinski]

Short-term, you can add this directory "notebooks" and move "Examples.ipynb" there.