Update documentation to have additional details like how to add seria…

…lizer/deserializer.

docs/custom-json-serializers-deserializers.md

@@ -20,12 +20,15 @@ public class CustomJsonbService implements EventingService {
 
     @Override
     public Map<String, Jsonb> overrideJsonbConfig() {
-        JsonbConfig config = new JsonbConfig().withDateFormat("MM dd yyyy HH:mm Z", null);
+        JsonbConfig config = new JsonbConfig().withDateFormat("MM dd yyyy HH:mm Z", null).withDeserializers(OBJECTID_DESERIALIZER).withSerializers(
+            OBJECTID_SERIALIZER);
         return Collections.singletonMap("MyModelClass.class.getName()", JsonbBuilder.create(config));
     }
 }
 ```
 
+We can customize the JsonbConfig as per our need in above example we have registered additional serializer and date formatting for the class MyModelClass.
+
 As the discovery of eventing services uses the ServiceLoader mechanism, don't forget to add a 
 `META-INF/services/io.smallrye.graphql.spi.EventingService` file that contains the fully qualified 
 name of your implementation.