Distributed data parallel training for streaming datasets
### Feature request

Any documentations for the the `load_dataset(streaming=True)` for (multi-node multi-GPU) DDP training? 

### Motivation

Given a bunch of data files, it is expected to split them onto different GPUs. Is there a guide or documentation?

### Your contribution

Does it requires manually split on data files for each worker in `DatasetBuilder._split_generator()`? What is`IterableDatasetShard` expected to do?