Update ingress docs to have more up to date code examples (#2199)

Closes #2196

docs/customizations/exposing-prometheus-alertmanager-grafana-ingress.md

@@ -39,11 +39,13 @@ Also, the applications provide external links to themselves in alerts and variou
 
 ```jsonnet
 local kp =
-  (import 'kube-prometheus/kube-prometheus.libsonnet') +
+  (import 'kube-prometheus/main.libsonnet') +
   {
-    _config+:: {
+    values+:: {
+      common+: {
         namespace: 'monitoring',
       },
+    },
     prometheus+:: {
       prometheus+: {
         spec+: {
@@ -95,6 +97,7 @@ local kp =
     },
   };
 
+// Output a kubernetes List object with both ingresses (k8s-libsonnet)
 k.core.v1.list.new([
   kp.ingress['prometheus-k8s'],
   kp.ingress['basic-auth-secret'],