docs(docker): explain how to persist DNS configuration

docs/developer/setup/docker.md

@@ -116,7 +116,44 @@ Then run the network services to access the running containers.
    sudo resolvectl domain docker0 '~funkwhale.test.'
    ```
 
-   Please refer to the manual of your distribution for other configurations.
+   This is a temporary setting that will be lost after a reboot.
+
+   A superuser of the system can persist this setting by providing a
+   systemd service that `BindsTo=` the `docker0` device. This requires `sudo`
+   privilege.
+
+   ```sh
+   sudo sh -c "umask 133; tee /etc/systemd/system/funkwhale-dns-docker0.service" <<< "[Unit]
+   Description=Funkwhale per-link DNS configuration for docker0
+   BindsTo=sys-subsystem-net-devices-docker0.device
+   After=sys-subsystem-net-devices-docker0.device
+
+   [Service]
+   Type=oneshot
+   ExecStart=/usr/bin/resolvectl dns docker0 172.17.0.1
+   ExecStart=/usr/bin/resolvectl domain docker0 '~funkwhale.test.'
+   ExecStopPost=/usr/bin/resolvectl revert docker0
+   RemainAfterExit=yes
+
+   [Install]
+   WantedBy=sys-subsystem-net-devices-docker0.device
+   "
+   sudo systemctl daemon-reload
+   sudo systemctl enable --now funkwhale-dns-docker0.service
+   ```
+
+   This gives you a systemd unit, whose life cycle is bound to the `docker0`
+   network device.
+
+   ```sh
+   systemctl status \
+     funkwhale-dns-docker0.service \
+     sys-subsystem-net-devices-docker0.device
+   ```
+
+   Please refer to the manual of your distribution for other configurations,
+   e.g. with system installations of netplan, systemd-networkd, NetworkManager, resolvconf or dnsmasq. Ensure the search domain is set to `funkwhale.test.`
+   and the nameserver address is set to `172.17.0.1`.
 
    :::