Clarifying pagerduty
Should help clear up the following internal issues:
https://dev.gitlab.org/gitlab/organization/issues/651
https://dev.gitlab.org/gitlab/organization/issues/666
https://dev.gitlab.org/gitlab/organization/issues/667
\cc @balameb @kelvinmutuma @cabargas @patricio @dblessing @pcarranza @marin @jacobvosmaer @tmaczukin @jnijhof @sytses