Set the redirect for the root / of a custom domain

[metmarkosaric]

"can you add an option to set the redirect when someone visits the root / of a custom domain? or at least forward it to the tracked domain instead of an nginx 404?"

(feedback via email)

[cassidyjames]

This would alleviate #92 for elementary, at least, as we could build a custom sort of “dashboard” page that lists all our public stats pages, i.e. at elementary.io/stats. And then if someone is poking at the source/requests and wonders what stats.elementary.io is, they'd at least get something instead of a 404.

[ukutaht]

Thanks @cassidyjames, that makes sense.