adding documentation for notifyClose best pratices (#60)

* adding documentation for notifyClose best pratices

* adding documentation for notifyClose best pratices

* fix doc

Co-authored-by: Daniele Palaia <dpalaia@dpalaia-a02.vmware.com>

doc.go

@@ -104,5 +104,43 @@ encounters an amqp:// scheme.
 
 SSL/TLS in RabbitMQ is documented here: http://www.rabbitmq.com/ssl.html
 
+Best practises for Connections and Channels notifications.
+In order to be notified when a connection or channel gets closed both the structures offer the possibility to register channels using the `notifyClose` function like:
+notifyConnClose := make(chan *amqp.Error)
+conn.NotifyClose(notifyConnClose)
+No errors will be sent in case of a graceful connection close.
+In case of a non-graceful close, because of a network issue of forced disconnection from the UI, the error will be notified synchronously by the library.
+You can see that in the shutdown function of connection and channel (see connection.go and channel.go)
+ ```
+ if err != nil {
+      for _, c := range c.closes {
+        c <- err
+      }
+    }
+```
+The error is sent synchronously to the channel so that the flow will wait until the channel will be consumed by the caller.
+To avoid deadlocks it is necessary to consume the messages from the channels.
+This could be done inside a different goroutine with a select listening on the two channels inside a for loop like:
+```
+go func() {
+ for notifyConnClose != nil || notifyChanClose != nil {
+  select {
+   case err, ok := <-notifyConnClose:
+      if !(ok) {
+        notifyConnClose = nil
+      } else {
+        fmt.Printf("connection closed, error %s", err)
+      }
+   case err, ok := <-notifyChanClose:
+      if !(ok) {
+        notifyChanClose = nil
+      } else {
+        fmt.Printf("channel closed, error %s", err)
+      }
+    }
+ }
+}()
+```
 */
+
 package amqp091