Rust README

Make the README a concise landing page: what the project does, who it serves, which crate to choose, and where its maintained documentation lives. It is not an installation guide, a book contents page, or a copy of registry metadata.

Scope and write boundary

• Edit: create or revise only the requested READMEs and their authorized sources. Preserve unrelated edits and existing project identity.
• Review: audit or checklist requests report findings and proposed changes without modifying files. When write permission is ambiguous, choose Review. Use non-mutating checks or an isolated copy; do not run generators or formatters against the original checkout.