Add reminder to delete nginx-ingress ClusterRole

[mattwahner]

Proposed changes

When a user attempts to uninstall everything that is created in the nginx-ingress namespace, they may have not deleted the RBAC ClusterRole added in step 2. This note ensures they delete that role as well so that all resources are deleted when uninstalling nginx-ingress.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto master
• I will ensure my PR is targeting the master branch and pulling from my branch from my own fork

[Dean-Coakley]

Looks reasonable to me:
ClusterRole and ClusterRoleBinding are cluster wide/not namespaced resources and are not cleaned up by the kubectl delete namespace nginx-ingress command.

Thanks for the PR!

[pleshakov]

👍