add murano documentation

issue: https://github.com/ContainX/openstack4j/issues/830

as introduced in https://github.com/ContainX/openstack4j/pull/836, https://github.com/ContainX/openstack4j/pull/841, https://github.com/ContainX/openstack4j/pull/843
