Update the run --net cli help to include the 'host' option

and then add that to the run and cli docs

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Merge pull request #5622 from SvenDowideit/net-host-docs

Update the run --net cli help to include the 'host' option