Add warning about firewall configuration.

docs/ocis/getting-started.md

@@ -35,6 +35,10 @@ chmod +x ocis
 
 The default primary storage location is `/var/tmp/ocis`. You can change that value by configuration.
 
+{{< hint warning >}}
+oCIS internally uses mDNS. If your system has a firewall, make sure mDNS is allowed in your active zone.
+{{< /hint >}}
+
 
 ### Docker