Idea: Document snappy usage on server

[namxam]

Hi there, we are currently exploring kafka_ex in combination with snappy. It works quite nice, but we hit an issue when we deployed to a staging system. It was crashing because snappy nif was not loaded. We checked the setup again and again until we realized, that we had to put the snappy libs onto our deployment container as well. It was a really quick and easy fix, but finding the source caused us quite some headache.

I would submit a pull request for documentation, but I am not sure if you guys want to have that kind of info in there or where exactly to put it.

[joshuawscott]

I think the README would be a decent place to put that, maybe under the https://github.com/kafkaex/kafka_ex#compression section?