Correct application credential usage doc

There is a --restricted flag to counter the --unrestricted flag. It was
documented, but the usage example had missed it. Add it for
completeness.

Change-Id: Ib4cdcacdd16bfb59e9d18714106ecda99e418812

Author: cmurphy

doc/source/cli/command-objects/application-credentials.rst

@@ -21,7 +21,7 @@ Create new application credential
         [--role <role>]
         [--expiration <expiration>]
         [--description <description>]
-        [--unrestricted]
+        [--restricted|--unrestricted]
         <name>
 
 .. option:: --secret <secret>