Give a user feedback if the dataset he loads is streamable or not
**Is your feature request related to a problem? Please describe.**
I would love to know if a `dataset` is with the current implementation streamable or not. 

**Describe the solution you'd like**
We could show a warning when a dataset is loaded with `load_dataset('...',streaming=True)` when its lot streamable, e.g. if it is an archive. 

**Describe alternatives you've considered**
Add a new metadata tag for "streaming"
