ensure ddclient service is running; default protocols to []

- Add an explicit service state=started enabled=true task so the role is self-healing if the unit is disabled or stopped, rather than relying solely on the restart handler.
- Default ddclient_protocols to [] so the template's for-loop no longer errors when the var is omitted.
- README: note service management in the tagline and document the new ddclient_protocols default.

README.md

@@ -1,6 +1,6 @@
 # Ansible Role: ddclient
 
-Installs and configures ddclient for dynamic DNS updates.
+Installs ddclient, writes `/etc/ddclient.conf` and `/etc/default/ddclient`, and ensures the `ddclient` service is enabled and running.
 
 ## Example Playbook
 
@@ -59,6 +59,8 @@ Only applicable if using the IP detection method `fw`.
 
 ### Protocol Configuration
 
+`ddclient_protocols` is a list of DDNS provider entries. Defaults to `[]` — the role runs to completion but ddclient will have no updates to perform until you set it.
+
 **Common keys:**
 
 | Key | Required | Description |