swarm/src/behaviour: Fix outdated comment on derive's out_event (#2318)

The default behaviour changed with
#2214. This updates the doc
comment.

Initially raised in
#2290 (comment).

swarm/src/behaviour.rs

@@ -39,27 +39,23 @@ type THandlerInEvent<THandler> =
 ///
 /// Crate users can implement this trait by using the the `#[derive(NetworkBehaviour)]`
 /// proc macro re-exported by the `libp2p` crate. The macro generates a delegating `trait`
-/// implementation for the `struct`, which delegates method calls to all trait members.
+/// implementation for the `struct`, which delegates method calls to all struct members.
+///
+/// Struct members that don't implement [`NetworkBehaviour`] must be annotated with `#[behaviour(ignore)]`.
 ///
 /// By default the derive sets the [`NetworkBehaviour::OutEvent`] as `()` but this can be overridden
 /// with `#[behaviour(out_event = "AnotherType")]`.
 ///
-/// Struct members that don't implement [`NetworkBehaviour`] must be annotated with `#[behaviour(ignore)]`.
-///
-/// By default, events generated by the remaining members are delegated to [`NetworkBehaviourEventProcess`]
-/// implementations. Those must be provided by the user on the type that [`NetworkBehaviour`] is
-/// derived on.
+/// When setting a custom `out_event` users have to implement [`From`] converting from each of the
+/// event types generated by the struct members to the custom `out_event`.
 ///
-/// Alternatively, users can specify `#[behaviour(event_process = false)]`. In this case, users
-/// should provide a custom `out_event` and implement [`From`] for each of the event types generated
-/// by the struct members.
-/// Not processing events within the derived [`NetworkBehaviour`] will cause them to be emitted as
-/// part of polling the swarm in [`SwarmEvent::Behaviour`](crate::SwarmEvent::Behaviour).
+/// Alternatively, users can specify `#[behaviour(event_process = true)]`. Events generated by the
+/// struct members are delegated to [`NetworkBehaviourEventProcess`] implementations. Those must be
+/// provided by the user on the type that [`NetworkBehaviour`] is derived on.
 ///
-/// Optionally one can provide a custom `poll` function through the `#[behaviour(poll_method = "poll")]`
-/// attribute.
-/// This function must have the same signature as the [`NetworkBehaviour#poll`] function and will
-/// be called last within the generated [`NetworkBehaviour`] implementation.
+/// Optionally one can provide a custom `poll` function through the `#[behaviour(poll_method =
+/// "poll")]` attribute. This function must have the same signature as the [`NetworkBehaviour#poll`]
+/// function and will be called last within the generated [`NetworkBehaviour`] implementation.
 pub trait NetworkBehaviour: Send + 'static {
     /// Handler for all the protocols the network behaviour supports.
     type ProtocolsHandler: IntoProtocolsHandler;