Update cert-based auth documentation to use possible new options

I think this provides all existing functionality. To reproduce the list at the bottom of the previous docs:

#### Daemon modes
- `--auth=cert`, `--auth-ca`, `--auth-cert`, `--auth-key` set: Authenticate clients		
- `--auth=cert`, `--auth-cert`, `--auth-key`: Do not authenticate clients		
	
#### Client modes

- `--auth=cert`: Authenticate server based on public/default CA pool		
- `--auth=cert`, `--auth-ca`: Authenticate server based on given CA		
- `--auth=cert`, `--auth-cert`, `--auth-key`: Authenticate with client certificate, do not authenticate server based on given CA		
- `--auth=cert`, `--auth-ca`, `--auth-cert`, `--auth-key`: Authenticate with client certificate and authenticate server based on given CA