Update inaccurate section headers for backing up/restoring volumes (#13860)
Update inaccurate section headers for backing up/restoring volumes (#13860)

* Change section headers for backing up/restoring volumes to use "volume" instead of "container"

The section headers "Backup a container" and "Restore container from backup" are used as headers for sections that are actually about backing up and restoring volumes.

* Minor style update

Co-authored-by: Usha Mandya <63fc8324d194bb900191b7ad7215ea10fd135fb2@users.noreply.github.com>
docker/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io