help text for juju get-constraints needs improving

[Peter Matulis]

e.g.:

Usage: juju get-constraints [options] <service>

Summary:
Displays machine constraints for a service.

Options:

--format (= constraints)
    Specify output format (constraints|json|yaml)
-m, --model (= "")
    Model to operate in
-o, --output (= "")
    Specify output file

Details:
Shows machine constraints that have been set for a service with `juju set-constraints`.
By default, the model is the current model.
Service constraints are combined with model constraints, set with `juju set-model-constraints`, for commands (such as 'deploy') that provision machines for services. Where model and service constraints overlap, the service constraints take precedence.
Constraints for a specific model can be viewed with `juju get-model-constraints`.

Examples:

    juju get-constraints mysql
    juju get-constraints -m mymodel apache2

See also: set-constraints
          get-model-constraints
          set-model-constraints

[Reed O'Brien (reedobrien)]

PR: https://github.com/juju/juju/pull/5117