In 2a5c116f the `Usage:\n rails COMMAND`
was removed from the help USAGE file. The original PR
https://github.com/rails/rails/pull/27601 doesn't mention why this was
done, so I'm not sure if this was done by accident.

Most commands have help usages of the form:
```console
Usage:
  bin/rails notes [options]

....
```

...so it is more consistent to use this for help as well.
This also allows differentiating between `rails` outside application
directories and `bin/rails` inside application directories.