improve the help in cli to indicate pass the /var/run/docker.sock

[larrycai]

I already pull the nate/dockviz, and am used to forget the complete command to run it like

docker run --rm -v /var/run/docker.sock:/var/run/docker.sock nate/dockviz images -t

Will be nice to give hints or help when I just type

docker run nate/dockviz
docker run nate/dockviz image

Like the output

docker@boot2docker:~$ docker run --rm nate/dockviz images
dial unix /var/run/docker.sock: no such file or directory
you may want to try docker run --rm -v /var/run/docker.sock:/var/run/docker.sock nate/dockviz images -t

Or simple add help for this besides image and container

Then as end user, I don't need to google to have complete command line

[justone]

I just released a new version of dockviz, so if you docker pull nate/dockviz and run it again there will be a helpful error message. I also added a help subcommand.

Thanks.