Add examples for a plain-YAML guestbook and kustomize guestbook

ksonnet-guestbook/environments/dev/main.jsonnet

@@ -0,0 +1,8 @@
+local base = import "base.libsonnet";
+// uncomment if you reference ksonnet-lib
+// local k = import "k.libsonnet";
+
+base + {
+  // Insert user-specified overrides here. For example if a component is named \"nginx-deployment\", you might have something like:\n")
+  // "nginx-deployment"+: k.deployment.mixin.metadata.labels({foo: "bar"})
+}