Add Heroku button for easiest transition from parse.com

[exalted]

I wish you could add a Heroku button to this project so that with a single click I could create my own parse.com instance on an heroku app and switch my apps to it with just changing the API url in my app somehow.

[exalted]

https://devcenter.heroku.com/articles/heroku-button

[gfosco]

This is actually being attempted here in the example server: parse-community/parse-server-example#8