Add more examples to Tensor type

[InAnYan]

I would like to see examples for every method in Tensor types.

That would be useful from people that came from PyTorch. Because Python language is highly dynamic and Rust is not, it's not easy to map PyTorch code to Rust with Burn

[InAnYan]

I would also be awesome if you could show how to use indexing, like there:

https://docs.rs/tch/latest/tch/index/index.html