fix doc information in the limit.rst

I check files in compute/v2, and I find there is a mistake, then
I fix it.

Change-Id: Ic17b9d5e64e4ed8b1d8e1476c73dd6d9365167fc

Author: zheng yin

doc/source/command-objects/limits.rst

@@ -15,7 +15,8 @@ Show compute and block storage limits
 .. code:: bash
 
     os limits show
-        --absolute [--reserved] | --rate
+        --absolute | --rate
+        [--reserved]
         [--project <project>]
         [--domain <domain>]