Clarify the sparse "docker port" output + doc, what maps to what

[thomas-k-git]

- What I did

- How I did it

- How to verify it

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "patch-1" git@github.com:thomas-klambauer/cli.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[thomas-k-git]

See https://docs.docker.com/engine/reference/commandline/port/#examples
Most people rate this doc page badly.(192 negative, 70 positive), assuming the same reason why I was annoyed, no explanation in what direction the mapping happens (contains first, host first?!)

[codecov-io]

Codecov Report

Merging #1420 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1420   +/-   ##
=======================================
  Coverage   54.26%   54.26%           
=======================================
  Files         289      289           
  Lines       19331    19331           
=======================================
  Hits        10490    10490           
  Misses       8165     8165           
  Partials      676      676