Update README.md

Author: apottere

README.md

@@ -56,6 +56,8 @@ GraphQLServlet servlet = new SimpleGraphQLServlet(schema, executionStrategy);
 GraphQLServlet servlet = new SimpleGraphQLServlet(schema, executionStrategy, operationListeners, servletListeners);
 ```
 
+## Operation and Servlet Listeners
+
 You can also add [operation listeners](https://github.com/graphql-java/graphql-java-servlet/blob/master/src/main/java/graphql/servlet/GraphQLOperationListener.java) and [servlet listeners](https://github.com/graphql-java/graphql-java-servlet/blob/master/src/main/java/graphql/servlet/GraphQLServletListener.java) to an existing servlet.
 These listeners provide hooks into query execution (before, on success, and on failure) and servlet execution (before, on error, and finally):
 ```java