Document manual migration of `unicorn` settings to `puma`
We need to ensure we clearly document that unicorn
settings will not be automatically migrated over to puma
. The best place for this is likely the upgrade notes, and then to make a reference from the Puma docs for now until we are past the migration period.
For reference, the upgrade notes I am referring to are like: https://docs.gitlab.com/omnibus/update/gitlab_12_changes.html.