add ddns helper script

bin/ddns

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+set -e
+set -u
+set -x
+
+function url() {
+  echo "https://svc.joker.com/nic/update?username=$1&password=$2&hostname=$3"
+}
+
+IFS=':'
+read -r user password < "${DDNS_CREDENTIALS:-/var/lib/ddns/credentials}"
+unset IFS
+
+curl_url=$(url "$user" "$password" bs.vpn.dadada.li)
+
+curl -4 "$curl_url"
+curl -6 "$curl_url"