BZ#2034410: Adding a note for namespace label

Author: skrthomas

modules/nw-metallb-installing-operator-cli.adoc

@@ -41,6 +41,13 @@ metadata:
 EOF
 ----
 
+. Optional: To ensure BGP and BFD metrics appear in Prometheus, you can label the namespace as in the following command:
++
+[source,terminal]
+----
+$ oc label ns metallb-system "openshift.io/cluster-monitoring=true"
+----
+
 . Create an Operator group custom resource in the namespace:
 +
 [source,terminal]
@@ -128,4 +135,3 @@ $ oc get clusterserviceversion -n metallb-system \
 Name                                  Phase
 metallb-operator.{product-version}.0-nnnnnnnnnnnn   Succeeded
 ----
-