help text for juju add-unit needs improving

[Nick Veitch]

e.g.

juju add-unit

Usage: juju add-unit [options] <service name>

Summary:
Adds one or more units to a deployed service.

Options:

-m, --model (= "")
 Model to operate in
-n, --num-units (= 1)
 Number of units to add
--to (= "")
 The machine and/or container to deploy the unit in (bypasses constraints)

Details:
Adding units to an existing service is a way to scale out that service. Many charms will seamlessly support horizontal scaling, others may need an additional service to facilitate load-balancing (check the individual charm documentation).
This command is applied to services that have already been deployed.
By default, services are deployed to newly provisioned machines in accordance with any service or model constraints. Alternatively, this command also supports the placement directive ("--to") for targeting specific machines or containers, which will bypass any existing constraints.

Examples:

Add five units of wordpress on five new machines:

   juju add-unit wordpress -n 5

Add one unit of mysql to the existing machine 23:

   juju add-unit mysql --to 23

Create a new LXC container on machine 7 and add one unit of mysql:

   Juju add-unit mysql --to lxc:7

Add a unit of mariadb to LXC container number 3 on machine 24:

   juju add-unit mariadb --to 24/lxc/3

See also: remove-unit

[Reed O'Brien (reedobrien)]

PR: https://github.com/juju/juju/pull/5121
RB: https://github.com/juju/juju/pull/5121