add load-balancer-address annotation doc (kubernetes#2110)

Author: zetaab

docs/openstack-cloud-controller-manager/expose-applications-using-loadbalancer-type-service.md

@@ -227,6 +227,11 @@ Request Body:
 
   This annotations explicitly sets a hostname in the status of the load balancer service.
 
+- `loadbalancer.openstack.org/load-balancer-address`
+  
+  This annotation is automatically added and it contains the floating ip address of the load balancer service.
+  When using `loadbalancer.openstack.org/hostname` annotation it is the only place to see the real address of the load balancer.
+
 ### Switching between Floating Subnets by using preconfigured Classes
 
 If you have multiple `FloatingIPPools` and/or `FloatingIPSubnets` it might be desirable to offer the user logical meanings for `LoadBalancers` like `internetFacing` or `DMZ` instead of requiring the user to select a dedicated network or subnet ID at the service object level as an annotation.