doc: Fix starting etcd gateway command using DNS.
@@ -60,7 +60,7 @@ infra2.example.com. 300 IN A 10.0.1.12
Start the etcd gateway to fetch the endpoints from the DNS SRV entries with the command:
```bash
-$ etcd gateway --discovery-srv=example.com
+$ etcd gateway start --discovery-srv=example.com
2016-08-16 11:21:18.867350 I | tcpproxy: ready to proxy client requests to [...]
```
