chore: add example for DynamoDB template

rel/i18n/emqx_bridge_dynamo.hocon

@@ -35,7 +35,9 @@ local_topic.label:
 """Local Topic"""
 
 template.desc:
-"""Template, the default value is empty. When this value is empty the whole message will be stored in the database"""
+"""Template, the default value is empty. When this value is empty the whole message will be stored in the database.<br>
+The template can be any valid json with placeholders and make sure all keys for table are here, example:<br>
+  {"id" : ${id}, "clientid" : ${clientid}, "data" : ${payload}}"""
 
 template.label:
 """Template"""