Heroku differentiate between production and staging app

Heroku differentiate between production and staging app

I'm creating a Play 2.1.3 web app and I have setup two environments in
Heroku, one for production and one for staging.
What is the easiest way to differentiate between the two environments? For
instance I don't want the search robots to index my staging app so I want
to add a robots.txt for staging but then it will also be added for
production when pushing the repo.
Should I have two local (app-prod and app-staging) Play applications with
separate git repos on my computer? Then I will have to keep the two
applications in sync. After verifying that the staging app on Heroku works
successfully I would have to sync those changes with my production app
locally on my computer (how do I do that with Git?) and then push those
changes to the production app on Heroku.