juju show-offer displayed usage is wrong

[Nick Veitch]

[updated description to include points from additional comments]

The help for the juju show-offer command states the usage as:

     juju show-offer [options]

in fact, the usage should be

     juju show-offer [options] [<controller>:]<offer URL>

Additionally, the help text includes some examples which no longer actually work. Suggest replacing with:

Usage: juju show-offer [options] [<controller>:]<offer url>

Summary:
Shows extended information about the offered application.

Options:
-B, --no-browser-login (= false)
    Do not use web browser for authentication
-c, --controller (= "")
    Controller to operate in
--format (= tabular)
    Specify output format (json|tabular|yaml)
-o, --output (= "")
    Specify an output file

Details:
This command is intended to enable users to learn more about the
application offered from a particular URL. In addition to the URL of
the offer, extra information is provided from the readme file of the
charm being offered.

Examples:
To show the extended information for the application 'prod' offered
from the model 'default' on the same Juju controller:

     juju show-offer default.prod

The supplied URL can also include a username where offers require them. This will be given as part of the URL retrieved from the
'juju find-offers' command. To show information for the application
'prod' from the model 'default' as the user 'admin':

    juju show-offer admin/default.prod

To show the information regarding the application 'prod' offered from
the model 'default' on an accessible controller named 'controller':

    juju show-offer controller:default.prod

See also:
  find-offers

[Anastasia (anastasia-macmood)]

PR against develop (2.3-b+): https://github.com/juju/juju/pull/8015