Add note on reoncilers in controller

user-guide/NephioControllerNotes.md

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+Notes on the Nephio Controller
+=============================
+
+# Reconcilers
+
+[Reconcilers](https://kubebyexample.com/learning-paths/operator-framework/operator-sdk-go/controller-reconcile-function) are used by Kubernetes to enforce the desired state of a CR.
+
+## The Nephio Reconciler Interface
+
+The nephio controller supports multiple reconcilers and allows reconcilers to be plugged in. To plug into the Nephio controller, a reconciler implements the [nephio reconciler interface](https://github.com/nephio-project/nephio/tree/main/controllers/pkg/reconcilers/reconciler-interface). Reconcilers register with the nephio reconciler interface when they start up.
+
+The reconcilers below are currently supported in the nephio controller:
+
+```
+./controllers/pkg/reconcilers/token/reconciler.go
+./controllers/pkg/reconcilers/repository/reconciler.go
+./controllers/pkg/reconcilers/bootstrap-packages/reconciler.go
+./controllers/pkg/reconcilers/vlan-specializer/reconciler.go
+./controllers/pkg/reconcilers/generic-specializer/reconciler.go
+./controllers/pkg/reconcilers/network/reconciler.go
+./controllers/pkg/reconcilers/ipam-specializer/reconciler.go
+./controllers/pkg/reconcilers/bootstrap-secret/reconciler.go
+./controllers/pkg/reconcilers/approval/reconciler.go
+```
+
+## Enabling Reconcilers
+
+To enable a particular reconciler, you pass an environment variable to the nephio controller at startup. The environment variable is of the form `ENABLE-<RECONCILER>` where `<RECONCILER>` is the name of the reconciler to enable in upper case. Therefore, to enable the `bootstrap-packages` reconciler, pass the `ENABLE_BOOTSTRAPPACKAGES` to the nephio controller. reconcilers are disabled by default.
+
+<details>
+<summary>You can see what reconcilers are enabled on the nephio controller using `kubectl`.</summary>
+
+```
+$ kubectl describe pod -n nephio-system nephio-controller-6565fd695d-44kld
+
+*** Truncated output ***
+
+Name:             nephio-controller-6565fd695d-44kld
+Containers:
+  controller:
+    Container ID:  containerd://37d3eff53c1944a659e5a7ab913173db42f34b44347072e6c9b51e5671f35ea2
+    Environment:
+      POD_NAMESPACE:              nephio-system (v1:metadata.namespace)
+      POD_IP:                      (v1:status.podIP)
+      POD_NAME:                   nephio-controller-6565fd695d-44kld (v1:metadata.name)
+      NODE_NAME:                   (v1:spec.nodeName)
+      NODE_IP:                     (v1:status.hostIP)
+      GIT_URL:                    http://172.18.0.200:3000
+      GIT_NAMESPACE:              gitea
+      ENABLE_APPROVAL:            true
+      ENABLE_REPOSITORIES:        true
+      ENABLE_BOOTSTRAPSECRETS:    true
+      ENABLE_BOOTSTRAPPACKAGES:   true
+      ENABLE_GENERICSPECIALIZER:  true
+      ENABLE_NETWORKS:            true
+      CLIENT_PROXY_ADDRESS:       resource-backend-controller-grpc-svc.backend-system.svc.cluster.local:9999
+```
+
+</details>
+
+To check that the reconcilers are actually deployed, you can examine the logs from the nephio controller. The log rolls over so you may need to redeploy the nephio controller to see what reconcilers are being deployed.
+
+```
+ $ kubectl rollout restart deployment nephio-controller -n nephio-system
+
+$ k logs -n nephio-system nephio-controller-59487989bf-md845 --all-containers | grep enable
+2023-06-27T11:37:58.646Z	INFO	setup	enabled reconcilers	{"reconcilers": "repositories,approval,bootstrappackages,bootstrapsecrets,genericspecializer,networks"}
+```
+