Adjust doc comment of Condvar::wait_while

The existing phrasing implies that a notification must be received for `wait_while` to return. The phrasing is changed to better reflect the behavior.

Author: rawler

library/std/src/sync/condvar.rs

@@ -195,8 +195,11 @@ impl Condvar {
 if poisoned {Err(PoisonError::new(guard))}else{Ok(guard)}
 }
 
-/// Blocks the current thread until this condition variable receives a
-/// notification and the provided condition is false.
+/// Blocks the current thread until the provided condition becomes false.
+///
+/// `condition` is checked immediately; if not met (returns `true`), this
+/// will [`wait`] for the next notification then check again. This repeats
+/// until `condition` returns `false`, in which case this function returns.
 ///
 /// This function will atomically unlock the mutex specified (represented by
 /// `guard`) and block the current thread. This means that any calls
@@ -210,6 +213,7 @@ impl Condvar {
 /// poisoned when this thread re-acquires the lock. For more information,
 /// see information about [poisoning] on the [`Mutex`] type.
 ///
+/// [`wait`]: Self::wait
 /// [`notify_one`]: Self::notify_one
 /// [`notify_all`]: Self::notify_all
 /// [poisoning]: super::Mutex#poisoning