Polish spring-boot-sample-cache README

Closes gh-5807

spring-boot-samples/spring-boot-sample-cache/README.adoc

@@ -9,6 +9,7 @@ abstraction is supported by many caching libraries, including:
 * `Infinispan`
 * `Couchbase`
 * `Redis`
+* `Caffeine`
 * `Guava`
 * Simple provider based on `ConcurrentHashMap`
 * Generic provider based on `org.springframework.Cache` bean definition(s)
@@ -62,6 +63,13 @@ used to configure the underlying `CacheManager`.
 
 
 
+=== EhCache 3.x
+Simply add the `org.ehcache:ehcache` dependency to the project. Since there is a
+default `ehcache.xml` configuration file at the root of the classpath, it is automatically
+used to configure the underlying `CacheManager`.
+
+
+
 === Hazelcast
 Both `com.hazelcast:hazelcast` and `com.hazelcast:hazelcast-spring` should be added to
 the project to enable support for Hazelcast.  Since there is a default `hazelcast.xml`