Add information about prometheus installation to admin readme

admin/README.md

@@ -219,3 +219,48 @@ ingress:
 
 Note: this annotation applies to the traefik ingress controller and may not
 be the same for nginx or other ingress controllers installed on a cluster.
+
+## Monitoring a cluster with Prometheus
+
+One of the best ways to fully monitor your cluster is to install Prometheus.
+Prometheus is itself a separate service for collecting metrics from various
+sources and presenting them to the user. One of the best ways to get this
+functionality on a Kubernetes cluster is by installing
+[Prometheus Operator](https://github.com/prometheus-operator/prometheus-operator).
+Prometheus Operator will install its own custom resources definitions (CRDs)
+to allow other applications to create their own ways of interacting with
+Prometheus.
+
+To install this on the Kubekorner K3s cluster we will use the stable
+prometheus-operator helm chart maintained by the helm community:
+
+https://github.com/helm/charts/tree/master/stable/prometheus-operator
+
+First we will create a namespace specifically for prometheus:
+
+```bash
+kubectl create namespace monitoring
+```
+
+Then we will install the helm chart in that namespace with the release name
+"prometheus-operator".
+
+```bash
+helm install -n monitoring prometheus-operator stable/prometheus-operator
+```
+
+Note, if your helm installation doesn't already have the stable chart
+repository added you may need to do:
+
+```bash
+helm repo add stable https://kubernetes-charts.storage.googleapis.com
+helm repo update
+```
+
+Also note at the time of writing this installation results in some warnings:
+
+```
+manifest_sorter.go:192: info: skipping unknown hook: "crd-install"
+```
+
+This is described in a GitHub issue here: https://github.com/helm/charts/issues/17511
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