DATAKV-213 - Update usage example for composed annotations using KeySpace.

We now mention an example using AliasFor that is used via AnnotatedElementUtils.findMergedAnnotation(…) to retrieve the keyspace value.

src/main/java/org/springframework/data/keyvalue/annotation/KeySpace.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014 the original author or authors.
+ * Copyright 2014-2018 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.
@@ -27,38 +27,46 @@ import org.springframework.data.annotation.Persistent;
 /**
  * Marker interface for methods with {@link Persistent} annotations indicating the presence of a dedicated keyspace the
  * entity should reside in. If present the value will be picked up for resolving the keyspace.
- * 
+ *
  * <pre>
  * <code>
  * &#64;Persistent
- * &#64;Documented
  * &#64;Retention(RetentionPolicy.RUNTIME)
  * &#64;Target({ ElementType.TYPE })
- * public &#64;interface Document {
- * 
- * 		&#64;KeySpace
- * 		String collection() default "person";
- * } 
+ * static @interface CacheCentricAnnotation {
+ *
+ *   &#64;AliasFor(annotation = KeySpace.class, attribute = "value")
+ *   String cacheRegion() default "";
+ * }
+ *
+ * &#64;CacheCentricAnnotation(cacheRegion = "customers")
+ * class Customer {
+ *   //...
+ * }
  * </code>
  * </pre>
- * 
+ *
  * Can also be directly used on types to indicate the keyspace.
- * 
+ *
  * <pre>
  * <code>
  * &#64;KeySpace("persons")
  * public class Foo {
- * 
- * } 
+ *
+ * }
  * </code>
  * </pre>
- * 
+ *
  * @author Christoph Strobl
+ * @author Mark Paluch
  */
 @Documented
 @Retention(RetentionPolicy.RUNTIME)
 @Target(value = { METHOD, TYPE })
 public @interface KeySpace {
 
+	/**
+	 * @return dedicated keyspace the entity should reside in.
+	 */
 	String value() default "";
 }