Add missing step to in-cluster-client-configuration example
Add missing step to in-cluster-client-configuration example

If the permissions are not setup correctly the example fails.

Change-Id: I167ef68be66f8b56740236ae475c3b7fdcc0dfb5

Kubernetes-commit: d222c310aaa4ce8777094f4a37a920982aff794d

li-ang/client-go,kubernetes/client-go