docs: Install openstack-client with upper constraints

Change-Id: I0419c68c18597bba4ff894b0a6c4a5ec007a8b4a
Signed-off-by: Adrian Andreias <[email protected]>
(cherry picked from commit 16acc3e)

Author: adrianandreias

doc/source/user/quickstart.rst

@@ -544,7 +544,7 @@ Using OpenStack
 
    .. code-block:: console
 
-      pip install python-openstackclient
+      pip install python-openstackclient -c https://releases.openstack.org/constraints/upper/|KOLLA_OPENSTACK_RELEASE|
 
 #. OpenStack requires an openrc file where credentials for admin user
    are set. To generate this file: