Extend usage docs
Extend usage docs

Bugs=222066508

Change-Id: Id6d3d7016f10097bf8cb48173cb34b090947a7e9
GitOrigin-RevId: 06adab2255455c1fc70f78296f30fb89d40e3219

GoogleCloudPlatform/gcpdiag,GoogleCloudPlatform/gcpdiag,GoogleCloudPlatform/gcpdiag