Allows the user to use `pretty` as the format string.
This enables users to put custom format options into their CLI config
just like is supported for `docker ps` and `docker images`
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Better formatting for usage template.
Group commands in usage to management/operation commands.
Remove the word Docker from the description of management commands.
Signed-off-by: Daniel Nephin <dnephin@docker.com>