refactor(grafana): update cluster dashboard (#4980)

grafana/README.md

@@ -5,6 +5,13 @@ GreptimeDB's official Grafana dashboard.
 
 Status notify: we are still working on this config. It's expected to change frequently in the recent days. Please feel free to submit your feedback and/or contribution to this dashboard 🤗
 
+If you use Helm [chart](https://github.com/GreptimeTeam/helm-charts) to deploy GreptimeDB cluster, you can enable self-monitoring by setting the following values in your Helm chart:
+
+- `monitoring.enabled=true`: Deploys a standalone GreptimeDB instance dedicated to monitoring the cluster;
+- `grafana.enabled=true`: Deploys Grafana and automatically imports the monitoring dashboard;
+
+The standalone GreptimeDB instance will collect metrics from your cluster and the dashboard will be available in the Grafana UI. For detailed deployment instructions, please refer to our [Kubernetes deployment guide](https://docs.greptime.com/nightly/user-guide/deployments/deploy-on-kubernetes/getting-started).
+
 # How to use
 
 ## `greptimedb.json`