Added example notebooks

[IvanSpirandelli]

No description provided.

[kalmarek]

I had a look at those notebooks and they seem to be ok.
I would prefer a separate folder with Project/Manifest.toml fixing the environment.

[saschatimme]

Not related to this particular PR, but we should also update or delete the other example notebook.
(Or use something like Literate.jl to also integrate them into CI).

[kalmarek]

the other notebook is kept by @micjoswig here:
https://github.com/micjoswig/oscar-notebooks/blob/master/polymake/g-vectors_of_random_simplicial_6-polytopes.ipynb
@micjoswig maybe those notebooks created by @IvanSpirandelli should go there as well?

I like @saschatimme suggestion about using Literate.jl though

[benlorenz]

I would prefer to have them here in the Polymake.jl repository (or a new repo under oscar-system), and they should be tested automatically, see #268.

[IvanSpirandelli]

I added the tomls and created folders for the examples.