--help CALL should show require arguments in usage

```
---> oapi-cli --help CreateVms
Usage: oapi-cli CreateVms [options]
...
```

should show 
```
---> oapi-cli --help CreateVms
Usage: oapi-cli CreateVms --ImageId ID [options]
...
```

there's already a line about require arguments, but it's hidden in the description. 