Add information about usage of external snapshots
Add information about usage of external snapshots

Change-Id: Idc4f1387545476f1642ba98483af36560a9d2d13

stackforge/fuel-web,eayunstack/fuel-web,stackforge/fuel-web,huntxu/fuel-web,huntxu/fuel-web,eayunstack/fuel-web,eayunstack/fuel-web,huntxu/fuel-web,stackforge/fuel-web,huntxu/fuel-web,eayunstack/fuel-web,eayunstack/fuel-web,huntxu/fuel-web