adjust documentation

src/lib.rs

@@ -480,7 +480,7 @@ impl<T> Event<T> {
  inner
  }
 
- /// Return the listener count
+ /// Return the listener count by aquiring a lock
  /// This is just a snapshot of the number of listeners at this point in time. It is possible for the actual number to change at any point.
  /// The number should only ever be used as a hint.
  /// This is only available when `std` feature is enabled.