Small tweak to middleware docs (#460)

pkg/middlewares/datachannel/README.md

@@ -19,6 +19,7 @@ func SubscriberAPI(next sfu.MessageProcessor) sfu.MessageProcessor {
 ### Init middlewares
 
 To initialize the middlewares you need to declare them after sfu initialization:
+
 ```go
 s := sfu.NewSFU(conf)
 dc := s.NewDatachannel(sfu.APIChannelLabel)
@@ -27,4 +28,5 @@ dc.Use(datachannel.KeepAlive(5*time.Second), datachannel.SubscriberAPI)
 dc.OnMessage(func(ctx context.Context, msg webrtc.DataChannelMessage, in *webrtc.DataChannel, out []*webrtc.DataChannel) {
 })
 ```
-The datachannels will be negotiated on peer join in the `Subscriber` peer connection.
+
+Datachannels created in this way will be negotiated on peer join in the `Subscriber` peer connection. Clients can then get a reference to the channel by using the `ondatachannel` event handler.