Improve documentation of max.task.idle.ms (kafka-streams)

max.task.idle.ms is an handy way to pause processing in a kafka-streams application. This is very useful when you need to join two topics that are out of sync, i.e when data in a topic may be produced before you receive join information in the other topic.

In the documentation, however, it is not specified that the value of max.task.idle.ms must be lower than max.poll.intervall.ms, otherwise you'll incur into an endless rebalancing problem.

I think it is better to clearly state this in the documentation.