Requires some environment variables to be provided. I used a git ignored envSource.sh for mine.
HEROKU_API_KEY
api key for doing stuff with heroku
WEB_APP
the name of the app to be hosted in heroku
TERRAFORM_STATE_APP
the name of the app just holding the terraform state in heroku
TERRAFORM_REMOTE_DB_URL
where we'll be storing the terraform state. You can get this after the pg db has been created