[cli] murano service-show command has no documentation string

[Timur Nurlygayanov]

Steps To Reproduce:
1. Login to the controller node with murano agent
2. Execute the following command:
murano help

Expected Result:
'murano help' will print the list of all available commands with some documentation string for each of them.

Observed Result:
We can't see ay documentatio string for command 'murano service-show':

...

Positional arguments:
  <subcommand>
    bundle-import Import a bundle.
    deployment-list List deployments for an environment.
    environment-create Create an environment.
    environment-delete Delete an environment.
    environment-list List the environments.
    environment-rename Rename an environment.
    environment-show Display environment details.
    package-create Create an application package.
    package-delete Delete a package.
    package-download Download a package to a filename or stdout.
    package-import Import a package.
    package-list List available packages.
    package-show Display details for a package.
    service-show
    bash-completion Prints all of the commands and options to stdout.
    help Display help about this program or one of its
                        subcommands.

...

[Ekaterina Chernova (efedorova)]

https://github.com/openstack/python-muranoclient/commit/dcc61f80213552f7fd2a5dfcc1e57d7bc11ec340