message: Add important context information to `handle_event` docs
diff: @@ -108,7 +108,7 @@ pub(crate) trait Component<REv> {
  /// Processes an event, outputting zero or more effects.
  ///
  /// This function must not ever perform any blocking or CPU intensive work, as it is expected
  - /// to return very quickly.
  + /// to return very quickly -- it will usually be called from an `async` function context.
  fn handle_event(
  &mut self,
  effect_builder: EffectBuilder<REv>,
  