[Docs] How to use with PyTorch page
_The documentation is not available anymore as the PR was closed or merged._
Currently the docs about PyTorch are scattered around different pages, and we were missing a place to explain more in depth how to use and optimize a dataset for PyTorch. This PR is related to #4457 which is the TF counterpart :)

cc @Rocketknight1 we can try to align both documentations contents now I think

cc @stevhliu let me know what you think !