📚 The doc issue

There are a few common steps that users often would like to do while preprocessing data, such as splitting their data set into train and eval. There are documentation in PyTorch Core about how to do these things with Dataset. We should add the same to our documentation, specifically for IterDataPipe. Or create a link to PyTorch Core's documentation for reference when that is appropriate. This issue is driven by common questions we have received either in person or on the forum.

If we find that any functionality is missing for IterDataPipe, we should implement them.