Add a small RAG reliability checklist (docs only, no code changes)

[onestardao]

Hi maintainers,

I recently contributed a small WFGY-related entry to ToolUniverse (merged into main). I noticed TxAgent is an agent-centric project where retrieval and tool results can become a reliability bottleneck, so I want to propose a very small, docs-only addition here.

Proposal (docs only):

1. Add a short “RAG Reliability Checklist” page under docs/ (or the preferred location).
2. The page is a practical checklist of common failure modes (query drift, evidence mismatch, overconfident synthesis, missing traceability), with simple reproduction prompts and troubleshooting steps.
3. Optional: a lightweight mapping table to a 16-mode diagnostic taxonomy (as labels only), so users can tag issues consistently. No claims, no enforcement, just tagging for clarity.

Why this fits:

• Improves debugging clarity for agent workflows
• No dependency on internal model decisions
• Easy to review and safe to merge or revert

If you agree with the direction, please point me to the preferred file location and any style conventions, and I can open a PR.

Thanks.