Document shortcomings of pypi-openstack element
Document shortcomings of pypi-openstack element

The element should not be used in production without considering these
facts. Also provide instructions for alternatives.

Change-Id: I2ed6c0ca1487506619128514f44e53738a76a6dc

rdo-management/tripleo-image-elements,radez/tripleo-image-elements,openstack/tripleo-image-elements,rdo-management/tripleo-image-elements,openstack/tripleo-image-elements,radez/tripleo-image-elements