Add cron schedules and sync docs

deploy/alertmanager/README.md

@@ -1,9 +1,18 @@
 # Alertmanager
 
-Placeholder for optional Alertmanager integration examples.
+Example Alertmanager configuration for the optional observability profile.
 
-Planned examples:
+`alertmanager.yml` is intentionally safe by default: it routes to a `null`
+receiver, so alerts are grouped but dropped. Before using it outside local
+development, add a real receiver and set `route.receiver` to that receiver.
 
-- receiver config for Monlet-originated alerts;
-- stable label conventions;
-- routing notes for avoiding duplicate notifications.
+Monlet can also send notifications to Alertmanager through the server notifier:
+
+```env
+MONLET_NOTIFIER_ALERTMANAGER_ENABLED=true
+MONLET_NOTIFIER_ALERTMANAGER_URL=http://alertmanager:9093
+```
+
+Keep labels stable and low-cardinality. The example groups by `alertname`,
+`agent_id`, and `check_id`; do not add timestamps, event IDs, or output text to
+Alertmanager labels.