Automatic merge from submit-queue

Update instructions for client staging copy

Following the existing instructions results in:

```
% ./staging/copy.sh
Do not run this script directly, but via hack/update-staging-client-go.sh.
```

Also format README.md as markdown.

**What this PR does / why we need it**: Updates docs to match reality

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: 

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```