add demo documentation

[abacaphiliac]

add demo documentation. user starts container named kafka with kafka as the ADVERTISED_HOST, creates a topic, starts a Producer in another container window, and starts a Consumer in another container window. Producer and Consumer will self-destruct when the user quits of the exec commands.

i thought i'd bring my findings back to this project, since i ran into the same n00b issues as some users here:
#49

copied from a gist i made this morning:
https://gist.github.com/abacaphiliac/f0553548f9c577214d16290c2e751071

no sweat if you think these docs don't belong in your project. thanks for making a very simple container to work with : )

[abacaphiliac]

thanks to @kpankonen for helping me understand how ADVERTISED_HOST affects other containers.

[gg7]

I don't see why most people (anyone?) would bother with ADVERTISED_HOST. Not only is advertised.host.name deprecated, but you most likely won't need it. Running my fork (Kafka 0.10.1.1 and other improvements):

docker run -d --name kafka --hostname kafka gg77/kafka
docker exec -it kafka /bin/bash -c "echo 'get /brokers/ids/0' | ~kafka/kafka/bin/zookeeper-shell.sh localhost:2181" | grep endpoints
{"jmx_port":-1,"timestamp":"1484877403562","endpoints":["PLAINTEXT://kafka:9092"],"host":"kafka","version":3,"port":9092}

What am I missing?

[abacaphiliac]

@gg7 thanks for the tip regarding deprecation. i wasn't aware. i'm new to Kafka and found this project to be the easiest to work with out of the small set i tried.