Add a Pull Request template
Add a Pull Request template

To try and help prevent the notification noise from PRs being opened
against upstream by mistake.

ad-m/heroku-buildpack-python,AltSchool/heroku-buildpack-python,Scalingo/python-buildpack,benjaminfox/heroku-buildpack-python-geoip,skilljar/heroku-buildpack-python,benjaminfox/heroku-buildpack-python-geoip,benmurden/heroku-buildpack-python-ember,benmurden/heroku-buildpack-python-ember,Scalingo/python-buildpack,edmorley/heroku-buildpack-python,heroku/heroku-buildpack-python,heroku/heroku-buildpack-python,ad-m/heroku-buildpack-python,AltSchool/heroku-buildpack-python