Merge pull request #438 from dgrisonnet/update-customizing-section

Add note related to example.jsonnet in README

README.md

@@ -174,6 +174,8 @@ e.g. of how to compile the manifests: `./build.sh example.jsonnet`
 
 Here's [example.jsonnet](example.jsonnet):
 
+> Note: some of the following components must be configured beforehand. See [configuration](#configuration) and [customization-examples](#customization-examples).
+
 [embedmd]:# (example.jsonnet)
 ```jsonnet
 local kp =