Add tutorials written in Pluto

[CarloLucibello]

We can port these tutorials to GNN.jl:

• https://pytorch-geometric.readthedocs.io/en/latest/notes/colabs.html
• https://antoniolonga.github.io/Pytorch_geometric_tutorials/

To set up Pluto + Documenter, see this repo:
https://github.com/JuliaManifolds/Manopt.jl

[CarloLucibello]

See also #173 for more ideas

[Dsantra92]

Maybe add an option to download the pluto file also?

[Dsantra92]

Is Pluto the best thing for tutorials?

Building the Static HTML file involves running the whole Pluto notebook (to get outputs and stuff). This rendering can often make life difficult for our CI. On the other hand, if we render the file in HTML locally and commit it, we lose the whole purpose of using Pluto.jl.

[CarloLucibello]

closing this as completed