improve wording of Waker::wake documentation

Author: rkuhn

library/core/src/task/wake.rs

@@ -220,12 +220,14 @@ unsafe impl Sync for Waker {}
 impl Waker {
     /// Wake up the task associated with this `Waker`.
     ///
-    /// Multiple wake-ups (through clones of this `Waker` or `wake_by_ref`) may be
-    /// coalesced into a single `poll` invocation by the runtime, and as long as
-    /// the runtime keeps running and the task is not finished it is expected that
-    /// each wake-up is followed by an invocation of `poll`, even in the absence of
-    /// other events. This makes it possible to yield to other tasks when running
-    /// potentially unbounded processing loops in order to maintain fairness.
+    /// As long as the runtime keeps running and the task is not finished, it is
+    /// guaranteed that each invocation of `wake` (or `wake_by_ref`) will be followed
+    /// by at least one `poll` of the task to which this `Waker` belongs. This makes
+    /// it possible to temporarily yield to other tasks while running potentially
+    /// unbounded processing loops.
+    ///
+    /// Note that the above implies that multiple wake-ups may be coalesced into a
+    /// single `poll` invocation by the runtime.
     #[inline]
     #[stable(feature = "futures_api", since = "1.36.0")]
     pub fn wake(self) {