fix(helm): improve documentation

Author: genofire

helm/dendrite/.helm-docs/monitoring.gotmpl

@@ -5,6 +5,11 @@
 
 * Works well with [Prometheus Operator](https://prometheus-operator.dev/) ([Helmchart](https://artifacthub.io/packages/helm/prometheus-community/kube-prometheus-stack)) and their setup of [Grafana](https://grafana.com/grafana/), by enabling the following values:
 ```yaml
+dendrite_config:
+  global:
+    metrics:
+      enabled: true
+
 prometheus:
   servicemonitor:
     enabled: true
@@ -19,4 +24,4 @@ grafana:
     enabled: true # will deploy default dashboards 
 ```
 PS: The label `release=kube-prometheus-stack` is setup with the helmchart of the Prometheus Operator. For Grafana Dashboards it may be necessary to enable scanning in the correct namespaces (or ALL), enabled by `sidecar.dashboards.searchNamespace` in [Helmchart of grafana](https://artifacthub.io/packages/helm/grafana/grafana) (which is part of PrometheusOperator, so `grafana.sidecar.dashboards.searchNamespace`) 
-{{ end }}
+{{ end }}