Adds TODO

Author: spencergibb

docs/modules/ROOT/pages/spring-cloud-gateway-server-mvc/writing-custom-predicates-and-filters.adoc

@@ -231,4 +231,6 @@ class RouteConfiguration {
 
 The above route will add a `X-Response-Id` header to the response. Note the use of the `after()` method, rather than `filter()`.
 
-// TODO: advanced topics such as attributes, beans and more
+// TODO: registering for configuration
+
+// TODO: advanced topics such as attributes, beans and more