Updating doc of unified limit
Updating doc of unified limit

Adding the details of maximum and minimum
values a user can set for default limit,
resource limit and resource name in the
unified limit doc.

Change-Id: I9655fb502b287ed7f0d381498252a24b417e5718
Related-patch: https://review.openstack.org/#/c/610479/

mahak/keystone,openstack/keystone,openstack/keystone,openstack/keystone,mahak/keystone,mahak/keystone