Add multicluster dashboards docs

Author: andrein

docs/multicluster-dashboards.md

@@ -0,0 +1,60 @@
+---
+weight: 660
+toc: true
+title: Multi-cluster dashboard support
+menu:
+    docs:
+        parent: kube
+lead: Enable multi-cluster dashboard support in grafana
+---
+
+#Prerequisites
+
+Let's say we have two clusters, `east` and `west`.
+
+Each prometheus cluster should have `externalLabels` configured:
+
+```jsonnet
+# east
+values+:: {
+  prometheus+: {
+    externalLabels: {
+      cluster: "east",
+    },
+  },
+}
+
+# west
+values+:: {
+  prometheus+: {
+    externalLabels: {
+      cluster: "west",
+    },
+  },
+}
+```
+
+# Enable multi cluster support
+
+At the time of writing, only kubernetes-mixin and node-mixin support this.
+
+```jsonnet
+values+:: {
+  nodeExporter+: {
+    mixin+: {
+      _config+: {
+        showMultiCluster: true,
+        # clusterLabel: '<cluster label, if different than the default "cluster">',
+      },
+    },
+  },  
+  kubernetesControlPlane+: {
+    mixin+: {
+      _config+: {
+        showMultiCluster: true,
+        # clusterLabel: '<cluster label, if different than the default "cluster">',
+      },
+    },
+  },
+}
+````