Automatic merge from submit-queue (batch tested with PRs 65987, 65962). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Add pod.yaml to user-guide

This is referenced in k/community for an example on how to run Kubernetes locally: https://github.com/kubernetes/community/blob/master/contributors/devel/running-locally.md#running-a-user-defined-pod.

It was removed earlier since it was thought as not used in https://github.com/kubernetes/kubernetes/pull/54342. This was the original `pod.yaml`: https://github.com/kubernetes/kubernetes/blob/668bedd9431d234b7471ac48748626885dc38232/test/fixtures/doc-yaml/user-guide/pod.yaml. This PR adds it back again.

Fixes https://github.com/kubernetes/community/issues/2351

**Release note**:

```release-note
NONE
```