Document that --port takes full listen address

[luisgerhorst]

Issue #, if available: NA

Description of changes: I considered adding a --listen flag and deprecating --port, however, this would make this simple change too complicated in my opinion.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[luisgerhorst]

The exact address format ListenAndServer accepts is documented here https://cs.opensource.google/go/go/+/refs/tags/go1.20.6:src/net/dial.go;l=284 (via https://cs.opensource.google/go/go/+/refs/tags/go1.20.6:src/net/http/server.go;l=2604).

[luisgerhorst]

It would be great to have this merged, as we rely on the feature and documenting it like this will ensure that it is not unintentionally removed in a future version.

[rapphil]

Thank you!