Fix detaching from attached container

Text was copied from man-pages https://raw.githubusercontent.com/docker/docker/master/docs/man/docker-attach.1.md

Signed-off-by: Jyrki Puttonen <jyrkiput@gmail.com>
Merge pull request #8124 from jyrkiput/patch-1

Fix detaching from attached container
Adding exec remote API documentation along with minor code cleanup.
Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)