This may just be a README issue, but it may also affect asset_sync's behavior when 'user-env-compile' gets yanked next week.
See discussion here: https://discussion.heroku.com/t/ruby-build-environment-variable-access/460
Note: All official buildpacks have been patched to support buildpack-env-arg
For those of us who use turbo-sprockets, a buildpack with the latest patch can be found here:
+1 came here to check on the status of this.