skaffold.yaml: annotate gcb profile

skaffold.yaml

@@ -42,6 +42,15 @@ deploy:
   kubectl:
     manifests:
     - ./kubernetes-manifests/**.yaml
+    
+# "gcb" profile allows building and pushing the images
+# on Google Container Builder without requiring docker
+# installed on the developer machine. However, note that
+# since GCB does not cache the builds, each build will
+# start from scratch and therefore take a long time.
+#
+# This is not used by default. To use it, run:
+#     skaffold run -p gcb
 profiles:
   - name: gcb
     build: