Document reason for two API Docs staging apps

> Siva
Yes it is intentional that this app doesn't have a custom domain on heroku
That's how we're able to route traffic through fastly

> locks
Siva bit of sidetrack, we have two staging apps but they seem to point to the same commit on the same branch

> Siva
one has a cdn config and another doesn't. the one which doesn't have a cdn config is used as a template for review apps.