add Quick start instructions and generalize $HOME path

[asashnov]

With these changes, I'm able to start my cluster.

Previously there was an error about the unknown argument 'kafka_path' in KafkaBrokerApp constructor.

The only thing I changed: by default, it will start with Kafka broker 2.2.0 (binary distribution) instead of cloning and building Kafka sources. I hope it will not disrupt the way you are used to working with this testing framework. But on the other hand, it will help new users start quickly.

[edenhill]

Can you fix the conflicts?