feature: the package installs the Router Manager, which is no longer a package of its own.

docs/dns.md

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+# DNS
+
+The router's name server (PowerDNS), the primary of the router's domains. Every domain has the
+same two name servers: the router's FQDN and a secondary name server. The [web sites](sites.md)
+whose DNS is Router managed get their records in the domain they are in.
+
+## Settings
+
+- **State:** disabled, running, or not running yet; the router installs PowerDNS when it is
+  enabled.
+- **Primary name server:** the router's FQDN, the SOA and the first NS of every domain. It is the
+  router's name and is not edited here; its own A record is kept by the DNS of its domain,
+  wherever that is, not by the router's domains.
+- **Secondary name server:** the second NS of every domain, required while the name server is
+  enabled. The router notifies the addresses it resolves to of every change and allows them to
+  transfer the domains.
+- **Public IP address:** the router's public IP, which the records of the sites with Public IP
+  take; empty when the router has none or no site uses it.
+- **Listen:** the interfaces port 53 is open on. While IKEv2 or OpenVPN remote access is enabled,
+  it must not share an interface with the clients' resolver, by default on the internal one.
+- **TTL:** how long resolvers keep the answers of a domain without its own TTL.
+
+**Settings** edits them.
+
+## Domains
+
+**Add domain** takes the domain and an optional TTL; the edit button changes the TTL, and the
+remove button removes a domain with its manual records. A domain inside another domain of the
+router is delegated from it.
+
+A domain the router hosts, for example `example.com`, with the router's FQDN `router.other.net`,
+the secondary `ns2.provider.net`, and a Router managed site of `www.example.com` and
+`example.com` with Public IP `203.0.113.10`:
+
+```text
+example.com.      SOA  router.other.net. hostmaster.example.com. <serial> 10800 3600 604800 300
+example.com.      NS   router.other.net.
+example.com.      NS   ns2.provider.net.
+example.com.      A    203.0.113.10
+www.example.com.  A    203.0.113.10
+```
+
+Selecting a domain shows:
+
+- **Records served:** what the name server answers, including the SOA and NS records.
+- **Manual records:** the records added with **Add record**: A, AAAA, CNAME, TXT, MX, SRV or CAA.
+  A name is relative to the domain, `@` for the domain itself. A record of a name and type the
+  domain already has from its name servers or its sites is not served.
+
+Changes are served after the router applies them, a few seconds later; **Refresh** shows them.
+
+## Delegation
+
+The parent of each domain must delegate it: NS records naming the router's FQDN and the secondary
+name server, and, for a name server inside the domain, its A record (a glue record), at the
+registrar or DNS provider of the parent.