Another Useful Reference for the Design and Documentation of Unsafe Code

Hi,

We are a group of researchers who have been working on unsafe Rust for the past few years. Last year, we drafted a document that systematically documents the safe usage of unsafe code, including criteria for soundness encapsulation and guidelines for safety documentation:

[rust-safety-standard](https://github.com/safer-rust/rust-safety-standard/blob/main/rust-safety-standard.md)

We hope this document can serve as a useful reference for the Unsafe Rust Review Skill in this repository.

If there is interest, we would be happy to submit a PR to include or reference it in the repository.

Read the linked rust-safety-standard.md and the repository's Unsafe Rust Review Skill materials first. Clarify whether the project wants to include the document or link to it, then identify the appropriate documentation location; done means an agreed reference or inclusion change, with scope confirmed by maintainers.

Written by the indexing model from the issue text.