docker config: correct the help output

Previously the help function output in the docker config listed port 80 as the port on which the server would listen for DNS over UDP and TCP. However that was inconsistent with the first output line where it was indicated to be port 53. This has now been corrected.

Originally submitted as https://github.com/CZ-NIC/knot-resolver/pull/60

enabled an automatic merge when the pipeline for da65cd50 succeeds

canceled the automatic merge

merged

mentioned in commit d5f80fc1