add doc comment for join handle drop behavior
@@ -46,6 +46,9 @@ impl fmt::Debug for Task {
/// A handle that awaits the result of a task.
///
+/// Dropping a [`JoinHandle`] will detach the task, meaning that there is no longer
+/// a handle to the task and no way to `join` on it.
+///
/// Created when a task is [spawned].
///
/// [spawned]: fn.spawn.html
