Update Custom Metrics Adapter docs with more current information about metrics naming
Update Custom Metrics Adapter docs with more current information about metrics naming

GoogleCloudPlatform/k8s-stackdriver,kawych/k8s-stackdriver,GoogleCloudPlatform/k8s-stackdriver,GoogleCloudPlatform/k8s-stackdriver,kawych/k8s-stackdriver,kawych/k8s-stackdriver,kawych/k8s-stackdriver