possible update/clarification to manifest.js readme section?

[josh-m-sharpe]

Not really a bug, but some thoughts on the manifest.js section of the README:

The readme states: If you've got a manifest.js file and you want to explicitly make sure an admin.js file is generated and made available to the public you can link it like this:

1. it seems that app/assets/config/manifest.js is required now. Without it, rake assets:precompile fails with Sprockets::Railtie::ManifestNeededError.
2. That said, a blank manifest.js seems to work 'just fine' - So why do we need it?
3. Even with a blank manifest.js all my assets that are defined by Rails.application.config.assets.precompile (the way they were in sprockets 3.7.1) are both compiled and available to the public -- which doesn't seem to follow from what is stated in the README

System configuration

sprockets 4.0.beta8 ruby 2.5.1

Thanks!