Clarified docs on non-atomic oprations on owned/mut refs to atomics

Author: peterjoel

library/core/src/sync/atomic.rs

@@ -28,7 +28,8 @@
 //! Basically, creating a *shared reference* to one of the Rust atomic types corresponds to creating
 //! an `atomic_ref` in C++; the `atomic_ref` is destroyed when the lifetime of the shared reference
 //! ends. (A Rust atomic type that is exclusively owned or behind a mutable reference does *not*
-//! correspond to an "atomic object" in C++, since it can be accessed via non-atomic operations.)
+//! correspond to an “atomic object” in C++, since the underlying primitive can be mutably accessed
+//! with `get_mut to perform non-atomic operations.)
 //!
 //! [cpp]: https://en.cppreference.com/w/cpp/atomic
 //!