update gcloud documentation
update gcloud documentation

PiperOrigin-RevId: 317348324
Change-Id: Icdbe8a1ef1e7d9d53d90db834a0131b52e5cf4d7

GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks