Document `CStr::as_ptr` dangers. r? @steveklabnik Hi! I've tried to document `CString::new("hello").unwrap().as_ptr()` footgun. Related [RFC] and the original [discussion]. [RFC]: https://github.com/rust-lang/rfcs/pull/1642 [discussion]: https://users.rust-lang.org/t/you-should-stop-telling-people-that-safe-rust-is-always-safe/6094