help text for 'ctrlc api get system' is incorrect

the help text says the command is: 

```
ctrlc get system --id 123e4567-e89b-12d3-a456-426614174000 --template='{{.id}}'
```

It should say: 

```
$ ctrlc get system -s 123e4567-e89b-12d3-a456-426614174000 --template='{{.id}}'
# or --system="123e4567-e89b-12d3-a456-426614174000"
```