docs: document some JSON parameters /containers/create and /containers/(id)/start in remote api (fixes #2948)

Docker-DCO-1.1-Signed-off-by: Manuel Woelker <github@manuel.woelker.org> (github: manuel-woelker)
Merge pull request #4245 from manuel-woelker/docs-remote-api

Added some documentation for the JSON params in the /containers/create and /containers/(id)/start remote APIs