Merge pull request #1545 from 31z4/zookeeper

Update Zookeeper documentation

zookeeper/content.md

@@ -30,7 +30,7 @@ $ docker run -it --rm --link some-zookeeper:zookeeper zookeeper zkCli.sh -server
 
 ## %%STACK%%
 
-This will start Zookeeper in [replicated mode](https://zookeeper.apache.org/doc/current/zookeeperStarted.html#sc_RunningReplicatedZooKeeper). Run `docker stack deploy -c stack.yml %%REPO%%` (or `docker-compose -f stack.yml up`) and wait for it to initialize completely. Ports `2181-2183` will be exposed.
+This will start Zookeeper 3.5 in [replicated mode](https://zookeeper.apache.org/doc/current/zookeeperStarted.html#sc_RunningReplicatedZooKeeper). Please note, that Zookeeper 3.4 has slightly different `ZOO_SERVERS` format. Run `docker stack deploy -c stack.yml %%REPO%%` (or `docker-compose -f stack.yml up`) and wait for it to initialize completely. Ports `2181-2183` will be exposed.
 
 > Please be aware that setting up multiple servers on a single machine will not create any redundancy. If something were to happen which caused the machine to die, all of the zookeeper servers would be offline. Full redundancy requires that each server have its own machine. It must be a completely separate physical server. Multiple virtual machines on the same physical host are still vulnerable to the complete failure of that host.