Fix help message of image add project

Only with the admin role you can use the project name with
'image add project'. With the normal member role you have to
use the project id instead. If you try to use the name, you
don't receive an error, but it won't work.

Change-Id: I2d11c07a256917d12c46a7c302c5a5e8752a1df0
Task: 29543
Story: 2002535

openstackclient/image/v2/image.py

@@ -86,7 +86,7 @@ class AddProjectToImage(command.ShowOne):
         parser.add_argument(
             "project",
             metavar="<project>",
-            help=_("Project to associate with image (name or ID)"),
+            help=_("Project to associate with image (ID)"),
         )
         common.add_project_domain_option_to_parser(parser)
         return parser