Examples in the documentation

[AntonioCarta]

We should add some examples in the classes documentation, at least for the high level classes and all the features more frequently used by the end user. I think pytorch documentation is really good at this (example) and most pytorch users expect the same quality.

See #885 for an example.

[niniack]

Is the idea that an Avalanche documentation page such as this about the SimpleCNN class would include an example similar to this

If I have got the idea, then I'm interested in contributing! If there is anything I should keep in mind to get started, please let me know.

[AntonioCarta]

Yes, that's what we want to achieve. I think you can start immediately, you don't need much background on avalanche to do it. You can make a PR once you have a couple of examples if you want some comments.