Clarify use of STUN and DOCKER_HOST_ADDRESS

[limitedAtonement]

The way the document currently reads, it appears that a user needs to specify a DOCKER_HOST_ADDRESS to let the software know about its public IP address, AND that public IP address will be discovered, which doesn't make sense.

I'm not sure how this exactly works, but my suggested verbiage is how I would like it to work. If my proposal isn't correct, please correct it to make the document more usable.