feat: add notes

src/content/docs/applications/coredns.mdx

@@ -13,3 +13,17 @@ hero:
       link: https://gitea.alexlebens.dev/alexlebens/infrastructure/src/branch/main/clusters/cl01tl/helm/coredns
       icon: right-arrow
 ---
+
+import { Aside } from '@astrojs/starlight/components';
+
+<Aside type="tip">Has an [Grafana Dashboard](https://grafana.alexlebens.net/goto/dfiq3jh1ez0n4a?orgId=1)</Aside>
+
+# Purpose
+
+DNS server just for cluster services, such as pod and service routing.
+
+# Notes
+
+Upstreams to [Blocky](https://docs.alexlebens.dev/applications/blocky/) for external DNS queries and also to the [Tailscale](https://docs.alexlebens.dev/applications/tailscale-operator/) DNS server for Tailnet access.
+
+Deploys as part of the Talos upgrades, but managed by Helm chart for the above custom configuration.