Readme tweaks

Hi there, I was running through the readme (excellent work!) using a logged-out browser and caught this. It seems that when you're logged in, the admin header loads the `drupal` and `once` js libraries. 

I added the two required core libraries to the `awesome.libraries.yml` example in the readme, as well as in `src/awesome/awesome.libraries.yml`, and updated the javascript filenames there to match `src/awesome`.

Note: my first pull request, please excuse me if I've done something incorrectly.