this line mentions `the 'source_root' class method` but when I look into the file I got:

```ruby
class Rails::MyHelperGenerator < Rails::Generators::NamedBase
  source_root File.expand_path('../templates', __FILE__)
end
```

As this is not a method definition but a method call I think we should reword it to:

> ... and the `source_root` class method call from ...