Add ribbon/zuul features and docs plus a sample

docs/src/main/asciidoc/README.adoc

@@ -2,8 +2,6 @@ image::https://api.travis-ci.org/spring-cloud/spring-cloud-sleuth.svg?branch=mas
 
 include::intro.adoc[]
 
-== This is a Developer Preview
-
 == Features
 
 * Adds trace and span ids to the Slf4J MDC, so you can extract all the logs from a given trace or span in a log aggregator. Example configuration:
@@ -17,22 +15,40 @@ logging:
 +
 (notice the `%X` entries from the MDC).
 
+* Optionally log span data in JSON format for harvesting in a log aggregator (set `spring.sleuth.log.json.enabled=true`).
+
 * Provides an abstraction over common distributed tracing data models: traces, spans (forming a DAG), annotations, key-value annotations. Loosely based on HTrace, but Zipkin (Dapper) compatible.
 
-* Instruments common ingress and egress points from Spring applications (servlet filter, rest template, scheduled actions).
+* Instruments common ingress and egress points from Spring applications (servlet filter, rest template, scheduled actions, message channels, zuul filters, feign client).
 
 * If `spring-cloud-sleuth-zipkin` then the app will generate and collect Zipkin-compatible traces (using Brave). By default it sends them via Thrift to a Zipkin collector service on localhost (port 9410). Configure the location of the service using `spring.zipkin.[host,port]`.
 
-== Running the sample
+== Running the samples
 
 1. Optionally run https://github.com/openzipkin/zipkin[Zipkin], e.g. via docker compose (there's a `docker-compose.yml` in https://github.com/spring-cloud-incubator/spring-cloud-sleuth[Spring Cloud Sleuth], or in https://github.com/openzipkin/docker-zipkin[Docker Zipkin]
-7. Run the sample application
+7. Run the zipkin sample application (and set `sample.zipkin.enabled=false` if you have no collector running)
 8. Hit `http://localhost:3380`, `http://localhost:3380/call`, `http://localhost:3380/async` for some interesting sample traces (the app callas back to itself).
 9. Goto `http://localhost:8082` for zipkin web (8080 if running locally from source, the host is the docker host, so if you are using boot2docker it will be different)
 
 WARNING: The docker images for zipkin are old and don't work very well (the UI in particular). Zipkin is in a state of flux, but it should settle down soon when there is an actual release. Best results actually come from building from source and running the jar files (the query and collector services need command line arguments, so check the zipkin README for updates).
 
-NOTE: You can see the zipkin spans without the UI (in logs) if you run the sample with `sleuth.sample.logging.collector.enabled=true`.
+NOTE: You can see the zipkin spans without the UI (in logs) if you run the sample with `sample.zipkin.enabled=false`.
+
+There are a few samples with slightly different features:
+
+* `spring-cloud-sleuth-sample`: vanilla (no zipkin) web app that calls back to itself on various endpoints ("/", "/call", "/async")
+
+* `spring-cloud-sleuth-sample-zipkin`: same as vanilla sample but with zipkin
+
+* `spring-cloud-sleuth-sample-messaging`: a Spring Integration application with two HTTP endpoints ("/" and "/xform")
+
+* `spring-cloud-sleuth-sample-ribbon`: two endpoints ("/" and "/call") that make calls to the "zipkin" sample via Ribbon. Also has `@EnableZUulProxy" so if the other samples are running they are proxied at "/messaging", "/zipkin", "/vanilla" (see "/routes" for a list).
+
+The Ribbon sample makes an interesting demo or playground for learning about zipkin. In the screenshot below you can see a trace with 3 spans - it starts in the "testSleuthRibbon" app and crosses to "testSleuthMessaging" for the next 2 spans.
+
+image::https://raw.githubusercontent.com/spring-cloud/spring-cloud-sleuth/master/docs/src/main/asciidoc/images/zipkin-trace-screenshot.png[Eample Zipkin Screenshot]
+
+> The fact that the first trace in says "testSleuthMessaging" seems to be a bug in the UI (it has some annotations from that service, but it originates in the "testSleuthRibbon" service).
 
 == Building