Tell Heroku How to Start Your App With Procfile

💡 If Heroku can't detect your app language you have to add a `Procfile` at the root of your project. The format is:

👉🏼 <process type>: <command>

A Node.js web server with index.js as entrypoint would have a Procfile with:

👉🏼 web: node index.js