#1852 Remote API documentation incorrect regarding private registries

Main issues:

- Remote API doco refers to "registry" parameter which is not supported
- Neglects to mention "tag" parameter which is supported
- Offers no guidance on pushing to private registries

Change only applied to v1.14 API documentation, if approved will retrofit to older versions as well.

Docker-DCO-1.1-Signed-off-by: Lachlan Coote <lachlan.t.coote@gmail.com> (github: lcoote)