Document how to add s3 credentials

[lbradstreet]

No description provided.

[fl00r]

For those, who are interested in this as well and have found only this issue

https://github.com/onyx-platform/onyx-amazon-s3/blob/0.10.x/src/onyx/s3/information_model.cljc#L11-L17

[MichaelDrogalis]

Most of the time you're going to want to use the AWS SDK ProviderChain to grab these from environment variables. Going through the catalog is somewhat of an escape hatch for when you can't use the env - it's less ideal because you're pushing credentials into ZooKeeper.

[fl00r]

I generally don't like the idea to access environment variables here and there. I prefer to capture all of them in my config and to pass them explicitly further.

[fl00r]

But your point about ZooKeeper is valid and important if you are exposing your ZooKeeper out of your private network.