text: Title: update doc.go in staging/ repositories
  Body: - Look at one of the directories under staging/src/k8s.io/ (Please don't pick more than one directory for one PR as it will cause issues for reviewers)
  - Find all the files named `doc.go` (example find staging/src/k8s.io/client-go/ -name doc.go)
  - See the following link it has a `// import "k8s.io/client-go/tools/remotecommand"` this tells tools how this package needs to be imported. So we should ensure that each doc.go has an import
     https://github.com/kubernetes/kubernetes/blob/1fc36a5743bc02d62ddaac6cd41b71f0ef191ce2/staging/src/k8s.io/client-go/tools/remotecommand/doc.go#L20
  - Add a description appropriate to the package (similar to the one below)
     https://github.com/kubernetes/kubernetes/blob/1fc36a5743bc02d62ddaac6cd41b71f0ef191ce2/staging/src/k8s.io/client-go/tools/remotecommand/doc.go#L17-L19
  - Look through sub directories and see if there are any other important directories that are likely to be used by outside users and add a doc.go
  
  Why are we doing this?
  - We perfer to use vanity urls instead of directly using github.com to refer to code, so this helps ensure that tools honor our wish. See https://golang.org/doc/go1.4#canonicalimports
  - It would be good to have some package level documentation since these directories under staging/ are meant to be for use by folks outside of kubernetes github org.
  
  /good-first-issue 