Add note to @CrossOrigin javadoc

Issue: SPR-13857

spring-web/src/main/java/org/springframework/web/bind/annotation/CrossOrigin.java

@@ -29,6 +29,14 @@ import org.springframework.core.annotation.AliasFor;
  *
  * <p>By default, all origins and headers are permitted.
  *
+ * <p><b>NOTE:</b> {@code @CrossOrigin} will only be processed if an an appropriate
+ * {@code HandlerMapping}-{@code HandlerAdapter} pair is configured such as the
+ * {@code RequestMappingHandlerMapping}-{@code RequestMappingHandlerAdapter} pair
+ * which are the default in the MVC Java config and the MVC namespace.
+ * In particular {@code @CrossOrigin} is not supported with the
+ * {@code DefaultAnnotationHandlerMapping}-{@code AnnotationMethodHandlerAdapter}
+ * pair both of which are also deprecated.
+ *
  * @author Russell Allen
  * @author Sebastien Deleuze
  * @author Sam Brannen