feat(alerting): add inital doc page

docs/sources/alerting/alerting.md

@@ -0,0 +1,14 @@
+---
+page_title: Alerting
+page_description: Alerting for Grafana
+page_keywords: alerting, grafana, plugins, documentation
+---
+
+# Alerting
+
+`status of alerting`
+
+Limitations.
+* no executor
+* only one alert per panel
+