README update re: Heroku's build process changes

[ekilah]

blog post: https://devcenter.heroku.com/changelog-items/1557
Extended FAQ: https://help.heroku.com/P5IMU3MP/heroku-node-js-build-script-change-faq

As far as I can tell, users of this repo will need to tell Heroku to skip running npm run build for them, because this buildpack takes care of that. Heroku's FAQ is pretty nice above, I'm suggesting a link out to it and/or a quick blurb in the README to say users should include heroku-postbuild in their package.json's scripts, as Heroku suggests.

[jmorrell]

👋 Hi, I wrote the FAQ and made the change

My hope is that once the buildpack is executing the build script, that this buildpack can do less work. If there's some issue with that I'm happy to help figure out a work-around.

[ekilah]

👋
To be honest, I inherited the build setup on the project I'm working on, so I'm not intimately familiar with which pieces are supposed to do which bits. but a change like that would require some messaging if other users of this repo are doing what I understood I should do, which is to tell Heroku to no longer run npm run build for me

[mars]

Hi folks 🤓 Revising this buildpack for the new build process is on my list to work on very soon. I’ll update with a testable PR when it’s ready 🙌

[mars]

Ready for testing ➡️ #156