Add MQTT listener and module in example config

ejabberd.yml.example

@@ -90,6 +90,11 @@ listen:
     ip: "::"
     module: ejabberd_http
     web_admin: true
+  -
+    port: 1883
+    ip: "::"
+    module: mod_mqtt
+    backlog: 1000
 
 s2s_use_starttls: optional
 
@@ -188,6 +193,7 @@ modules:
     ## db_type: sql
     assume_mam_usage: true
     default: always
+  mod_mqtt: {}
   mod_muc:
     access:
       - allow