Update documentation to use API auth

The updated instruction is not very user-friendly. I think the right
solution is to wrap the `/dns` commands in a `tools/dns.py` style
script, along the lines of `tools/mail.py`.

docs/index.md

@@ -58,7 +58,7 @@ For instance, in my case, I could tell my domain name registrar that `ns1.box.oc
 
 Optionally, to activate DNSSEC, you'll need to get a DS record from the box. While logged in on the box, run:
 
-	curl http://localhost:10222/dns/ds
+	sudo bash -c 'curl --user $(</var/lib/mailinabox/api.key): http://localhost:10222/dns/ds'
 
 This will print DS records for the domains that your box thinks it is the authoritative name server for. Copy the DS record and follow the DS record instructions provided by your domain name registrar.