Add documentation for how to leverage kustomize post rendering

Add documentation for customers for how to leverage kustomize post rendering to make changes to BigBang helm charts without requiring modification from BigBang

https://github.com/fluxcd/helm-controller/pull/202

marked #251 (closed) as a duplicate of this issue

marked this issue as related to #251 (closed)

added kinddocs priority6 labels

closed by !437 (merged)

closed