Docs for rawGrafanaDashboards filed

Propose in this https://github.com/brancz/kubernetes-grafana/pull/78

docs/developing-prometheus-rules-and-grafana-dashboards.md

@@ -310,3 +310,23 @@ local kp = (import 'kube-prometheus/kube-prometheus.libsonnet') + {
 { ['prometheus-' + name]: kp.prometheus[name] for name in std.objectFields(kp.prometheus) } +
 { ['grafana-' + name]: kp.grafana[name] for name in std.objectFields(kp.grafana) }
 ```
+
+Incase you have lots of json dashboard exported out from grafan UI the above approch is going to take lots of time. to improve performance we can use `rawGrafanaDashboards` field and provide it's value as json string by using importstr
+```jsonnet
+local kp = (import 'kube-prometheus/kube-prometheus.libsonnet') + {
+  _config+:: {
+    namespace: 'monitoring',
+  },
+  rawGrafanaDashboards+:: {
+    'my-dashboard.json': (importstr 'example-grafana-dashboard.json'),
+  },
+};
+
+{ ['00namespace-' + name]: kp.kubePrometheus[name] for name in std.objectFields(kp.kubePrometheus) } +
+{ ['0prometheus-operator-' + name]: kp.prometheusOperator[name] for name in std.objectFields(kp.prometheusOperator) } +
+{ ['node-exporter-' + name]: kp.nodeExporter[name] for name in std.objectFields(kp.nodeExporter) } +
+{ ['kube-state-metrics-' + name]: kp.kubeStateMetrics[name] for name in std.objectFields(kp.kubeStateMetrics) } +
+{ ['alertmanager-' + name]: kp.alertmanager[name] for name in std.objectFields(kp.alertmanager) } +
+{ ['prometheus-' + name]: kp.prometheus[name] for name in std.objectFields(kp.prometheus) } +
+{ ['grafana-' + name]: kp.grafana[name] for name in std.objectFields(kp.grafana) }
+```