Documentation: Remove reference to PUBLISH Dockerfile directive in networking docs

[deployable]

Proposed changes

Remove reference to PUBLISH Dockerfile directive in networking documentation as PUBLISH does not exist in the Dockerfile reference https://docs.docker.com/engine/reference/builder/

[johndmulhausen]

Good catch. Just so there's a note about what's possible when using config files, I think we should talk about the EXPOSE directive in Dockerfiles here, which are probably what the original writer meant.

[thaJeztah]

EXPOSE doesn't publish, so likely needs some extra words in that case

[mdlinville]

EXPOSE seems pretty useless really. I've been de-emphasizing it. I did a light edit to make this a teensy bit more clear.