Tunnels setup allow MITM attacks because of lack of authentication

[majormoses]

See: https://github.com/dnsimple/chef-stunnel/blob/2aefd996299dc18e8887b4bc7c57802a3d5bbf28/templates/default/stunnel.conf.erb#L43-L55

We need to expose these options and do some additional setup; until then we should add a big fat message in the readme about this as 99% are not gonna open the template to inspect every option and notice the commented out section.