Automatic merge from submit-queue
suggest use of `kube explain <resource>` in kube get output
**Release note**:
```release-note
release-note-none
```
This patch improves usability flow, making it easier for a user to
discover the command `kube explain <resource>` through `kube get` output.
##### After
```
$ kube get
You must specify the type of resource to get. Valid resource types include:
* componentstatuses (aka 'cs')
* configmaps (aka 'cm')
* daemonsets (aka 'ds')
* deployments (aka 'deploy')
* events (aka 'ev')
* endpoints (aka 'ep')
* horizontalpodautoscalers (aka 'hpa')
* ingress (aka 'ing')
* jobs
* limitranges (aka 'limits')
* nodes (aka 'no')
* namespaces (aka 'ns')
* petsets (alpha feature, may be unstable)
* pods (aka 'po')
* persistentvolumes (aka 'pv')
* persistentvolumeclaims (aka 'pvc')
* quota
* resourcequotas (aka 'quota')
* replicasets (aka 'rs')
* replicationcontrollers (aka 'rc')
* secrets
* serviceaccounts (aka 'sa')
* services (aka 'svc')
error: Required resource not specified.
Use "kubectl explain <resource>" for a detailed description of that resource (e.g. kubectl explain pods).
See 'kubectl get -h' for help and examples.
```
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