Update .info.yml and README for CKEditor 5

[alisonjo315]

First draft of how to do this -- please feel free to change with more / better steps!

• Update the commented-out example code in .info.yml
• "Create a child theme" instructions > Step 5: Update this step:
  • It'll be a scss file, not css (as in cwd_base).
  • Change name to ckeditor5.
  • No need for ckeditor templates js.