Add note to revert changes after completion
Add note to revert changes after completion

When the user did run a zero downtime upgrade, they might want to
revert the changes to make sure next upgrade will be as normal.

Closes https://gitlab.com/gitlab-org/omnibus-gitlab/issues/4649

gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab