Enhanced wording for coop paragraph in runtime compatiblity section

Co-authored-by: Alice Ryhl <aliceryhl@google.com>

tokio/src/sync/mod.rs

@@ -439,11 +439,8 @@
 //! or even use them from non-Tokio runtimes.
 //!
 //! When used in a Tokio runtime, the synchronization primitives participate in
-//! [cooperative scheduling](crate::task#cooperative-scheduling),
-//! periodically yielding back control to the runtime to avoid starving it.
-//! In a non-Tokio runtime, the yield points where control is handed back do
-//! nothing, not changing the behavior of the synchronization primitive in any
-//! way.
+//! [cooperative scheduling](crate::task#cooperative-scheduling) to avoid
+//! starvation. This feature does not apply when used from non-Tokio runtimes.
 //!
 //! The only exception to runtime compatibility is the
 //! [`mpsc::Sender::send_timeout`] method, which can't be called from non-Tokio