Document nodeattrib aliases

```python
_attraliases = {
    'bmc': 'hardwaremanagement.manager',
    'bmcuser': 'secret.hardwaremanagementuser',
    'switchuser': 'secret.hardwaremanagementuser',
    'bmcpass': 'secret.hardwaremanagementpassword',
    'switchpass': 'secret.hardwaremanagementpassword',
}
```

Check: https://github.com/xcat2/confluent/blob/master/confluent_client/confluent/client.py#L36-L42
