Add monitoring configuration deprecation notice

manifests/monitoring/README.md

@@ -0,0 +1,20 @@
+# :warning: Deprecation Notice
+
+Starting Flux v2.1.0, released August 24, 2023, the Flux monitoring
+configurations in this repository will be marked as deprecated. New monitoring
+docs are available at [Flux monitoring](https://fluxcd.io/flux/monitoring/)
+docs with new example configurations in
+[fluxcd/flux2-monitoring-example](https://github.com/fluxcd/flux2-monitoring-example/).
+The deprecated configurations will be removed in a future release of Flux. All
+users of these configurations are recommended to use the new monitoring setup,
+following the docs and the new examples.
+
+After collecting a lot of user feedback about our monitoring recommendation, in
+order to serve most of the needs of the users, we decided to create a new
+monitoring setup leveraging more of the kube-prometheus-stack, specifically
+kube-state-metrics, to enable configuring Flux custom metrics, see the [Flux
+custom Prometheus metrics](https://fluxcd.io/flux/monitoring/custom-metrics/)
+docs to learn more about it. Please refer to
+[fluxcd/flux2/4128](https://github.com/fluxcd/flux2/issues/4128) for a detailed
+explanation about this change and the new capabilities offered by the new
+monitoring setup.