Show instructions when password are pulled from secret resources

[etiennetremel]

Currently when a secret type Opaque is pulled from a secret (ie: password), it is converted in plain text and stored in the kustomization.yaml with a printf command, ie:

secretGenerator:
- commands:
    redis-password: printf \"OYTG9S4SUi\"
  name: sentry-redis
  type: Opaque

After the chart is deployed we need to warn the user that there is a plain text password stored there.