Clarify RequestMappingHandlerAdapter javadoc

This commit updates the javadoc of
`RequestMappingHanderAdapter.setCacheSecondsForSessionAttributeHandlers`
to explain how one can disable that feature and prevent "Cache-Control"
directives from being added when `@SessionAttributes` annotations are
used on Controllers.

Issue: SPR-13598

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapter.java

@@ -444,10 +444,18 @@ public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
 
 	/**
 	 * Cache content produced by {@code @SessionAttributes} annotated handlers
-	 * for the given number of seconds. Default is 0, preventing caching completely.
+	 * for the given number of seconds.
+	 * <p>Possible values are:
+	 * <ul>
+	 * <li>-1: no generation of cache-related headers</li>
+	 * <li>0 (default value): "Cache-Control: no-store" will prevent caching</li>
+	 * <li>> 0: "Cache-Control: max-age=seconds" will ask to cache content; not advised when dealing
+	 * with session attributes</li>
+	 * </ul>
 	 * <p>In contrast to the "cacheSeconds" property which will apply to all general
 	 * handlers (but not to {@code @SessionAttributes} annotated handlers),
 	 * this setting will apply to {@code @SessionAttributes} handlers only.
+	 *
 	 * @see #setCacheSeconds
 	 * @see org.springframework.web.bind.annotation.SessionAttributes
 	 */