Add Senlin-dashboard Train release notes
Add Senlin-dashboard Train release notes

Change-Id: I8fac49ccb20ca3b560ca95fb9443c142354a16e4

stackforge/senlin-dashboard,stackforge/senlin-dashboard,openstack/senlin-dashboard,openstack/senlin-dashboard,openstack/senlin-dashboard,openstack/senlin-dashboard,stackforge/senlin-dashboard