docker save: add and improve docs
docker save: add and improve docs

add usage examples for `docker save ...`

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)

cpuguy83/cli,thaJeztah/cli,e11137/cli,allencloud/cli,Zebrilee/cli,redpanda/cli,riyazdf/cli,dnephin/cli,thaJeztah/cli,Zebrilee/cli,ashfall/cli,riyazdf/cli,allencloud/cli,redpanda/cli,docker/cli,ashfall/cli,cpuguy83/cli,dnephin/cli,e11137/cli,docker/cli