Merge pull request jenkinsci/docker-inbound-agent#2 from chrishenzie/…

…UpdatingReadme

Adding udpate ECS container agent suggestion to README

README.md

@@ -6,6 +6,8 @@ A [Jenkins](https://jenkins-ci.org) slave using JNLP to establish connection.
 
 See [Jenkins Distributed builds](https://wiki.jenkins-ci.org/display/JENKINS/Distributed+builds) for more info.
 
+Make sure your ECS container agent is [updated](http://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs-agent-update.html) before running. Older versions do not properly handle the entryPoint parameter. See the [entryPoint](http://docs.aws.amazon.com/AmazonECS/latest/developerguide/task_definition_parameters.html#container_definitions) definition for more information.
+
 ## Running
 
 To run a Docker container