Is there a way to join multiple datasets in one?

**Is your feature request related to a problem? Please describe.**
I need to join 2 datasets, one that is in the hub and another I've created from my files. Is there an easy way to join these 2?

**Describe the solution you'd like**
Id like to join them with a merge or join method, just like pandas dataframes.

**Additional context**
If you want to extend an existing dataset with more data, for example for training a language model, you need that functionality. I've not found it in the documentation.