Doc: @EnableScheduling needs to be declared per application context

Issue: SPR-16852

Author: jhoeller

Diff for: spring-context/src/main/java/org/springframework/scheduling/annotation/EnableScheduling.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -187,6 +187,12 @@
  * but one demonstration how the code-based approach allows for maximum configurability
  * through direct access to actual componentry.<p>
  *
+ * <b>Note: {@code @EnableScheduling} applies to its local application context only,
+ * allowing for selective scheduling of beans at different levels.</b> Please redeclare
+ * {@code @EnableScheduling} in each individual context, e.g. the common root web
+ * application context and any separate {@code DispatcherServlet} application contexts,
+ * if you need to apply its behavior at multiple levels.
+ *
  * @author Chris Beams
  * @author Juergen Hoeller
  * @since 3.1