Added warning to the docs about the change in default behavior.

docs/src/main/asciidoc/spring-cloud-netflix.adoc

@@ -1078,6 +1078,10 @@ public class FooConfiguration {
 }
 ----
 
+WARNING:  Prior to the Spring Cloud Dalston release, if Hystrix was on the classpath Feign would have wrapped
+all methods in a circuit breaker by default.  This default behavior was changed in Spring Cloud Dalston in
+favor for an opt-in approach.
+
 [[spring-cloud-feign-hystrix-fallback]]
 === Feign Hystrix Fallbacks