text: Title: Docs: describe whether /learn is multi-modal
  Body: ### Problem
  
  The [learning about local data](https://jupyter-ai.readthedocs.io/en/latest/users/index.html#learning-about-local-data) do not state whether `/learn` is multi-modal and will use text + images. For instance, including plots generated in Jupyter notebooks can be extremely useful. Of course, multi-modal input would only be possible for the models that support the feature. 
  
  ### Proposed Solution
  
  It would be helpful if the docs clearly stated whether multi-modal input is used for `/learn`, at least for some models. 
  
  ### Additional context
  
  If `/learn` does not support multi-modal input, this would be a great feature to have.