Update auditing documentation.

Mention that even when only using the CreatedDate & LastModifiedDate annotations it is mandatory to enable auditing.

Closes #2283

Author: christophstrobl

src/main/asciidoc/auditing.adoc

@@ -4,6 +4,13 @@
 [[auditing.basics]]
 == Basics
 Spring Data provides sophisticated support to transparently keep track of who created or changed an entity and when the change happened. To benefit from that functionality, you have to equip your entity classes with auditing metadata that can be defined either using annotations or by implementing an interface.
+Additionally auditing has to be enabled either via Java or XML configuration which ensures required infrastructure components get registered.
+Please refer to the store specific section for configuration samples.
+
+[NOTE]
+====
+Applications that only track creation and modification dates do not need to specify an <<auditing.auditor-aware>>.
+====
 
 [[auditing.annotations]]
 === Annotation-based Auditing Metadata
@@ -19,7 +26,7 @@ class Customer {
   private User user;
 
   @CreatedDate
-  private DateTime createdDate;
+  private Instant createdDate;
 
   // … further properties omitted
 }