docs: fix description of `docker swarm join --help`
docs: fix description of `docker swarm join --help`

Signed-off-by: Kei Ohmura <82a3f76f5859104098e1c763aea3695df488375c@gmail.com>

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