Update docstring for RAG

[bishalgaire]

Initialize retriever in RAG generator

Proposed changes:

• ...

Status (please check what you already did):

• First draft (up for discussions & feedback)
• Final code
• Added tests
• Updated documentation

[brandenchan]

Hi @bishalgaire, in this PR I see you've changed the .md file for tutorial 7. This changes only how the tutorial will appear on our website (here).

To make the changes to the tutorials themselves, you'll need to make changes to tutorials/Tutorial7_RAG_Generator.py and tutorials/Tutorial7_RAG_Generator.ipynb.

Could you commit the same change to those files too?

[tholor]

Finishing this one as it was stale for quite a long time.
After a quick check, I believe we don't need to pass the retriever to the generator in the Tutorial as it's only needed if the documents that RAG gets in the predict() do not contain embeddings. In the tutorial we call update_embeddings(), so all docs should have the required embeddings.
@bishalgaire let us know if you faced any errors here with the original tutorial code.

done