Need more sample code

[colorzhang]

I have problems to run this demo:

1. embedding_pdf_documents can run on ray cluster as specified, it's good.
2. open_source_LLM_retrieval_qa instead only run on local ray
   The blog articles is not clear on how to run on ray cluster:

1. where to store faiss index? s3?
2. local files e.g. local_embeddings.py need to be specified by runtime_env, how?

Thanks