chore(rag): Document the indexing workflow

[erikleblanc]

Update README or Wiki with instructions on how to index documents in the RAG system (both manually and via #38’s script).

Wait for

#37 and #38 so the process is final.

Next Steps

#40 (Usage guide for retrieval logic) can reference or expand on these docs.

Checklist

• Explanation of how to set up environment, run the script.
• Mention any authentication or special endpoints.