docs: add source ranking to build and deploy docs

[KolaSailaja]

📌 Related Issue

Fixes #923

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📝 Description

This PR improves the build and deployment documentation by adding a dedicated section explaining RAG source ranking in LocalMind.

The documentation now covers:

• How retrieved document chunks are ranked using ChromaDB cosine similarity.
• How ranked chunks are used to generate document citations.
• The retrieval-related configuration options that influence source selection (rag_top_k and rag_chunk_overlap).
• Production considerations for configuring source retrieval while deploying LocalMind.

The changes are limited to the project documentation and do not modify any application code.

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📂 Files Changed

• README.md

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✅ Testing

• Verified Markdown formatting and heading hierarchy.
• Confirmed documentation is consistent with the existing repository structure.
• No code changes were introduced.

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📸 Screenshots

N/A (Documentation-only change)

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✔️ Checklist

• Documentation updated.
• No application code changed.
• Followed the existing documentation style.
• Kept the changes minimal to reduce merge conflicts.
• Verified Markdown formatting.
• Ready for review.

[vercel]

@KolaSailaja is attempting to deploy a commit to the Darshan's projects Team on Vercel.

A member of the Team first needs to authorize it.

[KolaSailaja]

@imDarshanGK Could you please review this pr and help me with the feedback about any changes needed

[imDarshanGK]

@KolaSailaja Thanks for the contribution! This PR doesn't match Issue #923. The issue is about updating the build and deploy documentation, but this PR adds documentation for RAG source ranking in the README. Please update the relevant build/deploy docs or link this PR to the appropriate issue instead.

[KolaSailaja]

@imDarshanGK I will do that