Compatibility with EhCache 3.0 M1 (as a JCache provider)

Issue: SPR-12847

spring-context-support/src/main/java/org/springframework/cache/ehcache/package-info.java

@@ -1,7 +1,12 @@
 /**
  * Support classes for the open source cache
- * <a href="http://ehcache.sourceforge.net">EhCache</a>,
+ * <a href="http://ehcache.sourceforge.net">EhCache 2.x</a>,
  * allowing to set up an EhCache CacheManager and Caches
  * as beans in a Spring context.
+ *
+ * <p>Note: EhCache 3.x lives in a different package namespace
+ * and is not covered by the traditional support classes here.
+ * Instead, consider using it through JCache (JSR-107), with
+ * Spring's support in {@link org.springframework.cache.jcache}.
  */
 package org.springframework.cache.ehcache;