Fix help string for gnt-group info

Signed-off-by: Bernardo Dal Seno <bdalseno@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>

lib/client/gnt_group.py

@@ -371,7 +371,8 @@ commands = {
     [TAG_SRC_OPT, PRIORITY_OPT, SUBMIT_OPT],
     "<group_name> tag...", "Remove tags from the given group"),
   "info": (
-    GroupInfo, ARGS_MANY_GROUPS, [], "<group_name>", "Show group information"),
+    GroupInfo, ARGS_MANY_GROUPS, [], "[<group_name>...]",
+    "Show group information"),
   }