explain how DNS zones get synced from LDAP a little more

tsa/howto/ldap.mdwn

@@ -15,6 +15,11 @@ the central LDAP server using the `sshdist` account, which means
 things keep working when LDAP is down. Most operations can be
 performed on the [db.torproject.org](https://db.torproject.org/) site or by [email](https://db.torproject.org/doc-mail.html).
 
+DNS zone files are also managed (at least partly) in LDAP. This is
+automated through cron jobs, but if you're in a hurry, the zones get
+generated by `ud-generate` on `alberti` (as `sshdist`?) and replicate
+(?) on `nevii` with `ud-replicate` (as `root`?).
+
 Handy commands
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