Add documentation to Signal::poll_wait(..).

embassy-util/src/channel/signal.rs

@@ -69,6 +69,7 @@ impl<T: Send> Signal<T> {
         })
     }
 
+    /// Manually poll the Signal future.
     pub fn poll_wait(&self, cx: &mut Context<'_>) -> Poll<T> {
         critical_section::with(|_| unsafe {
             let state = &mut *self.state.get();