subtheming guide on drupal-compose.org is missing essential steps [#2990910]

At the moment, the missing essential steps that I have documened are only as a comment in this issue: https://www.drupal.org/project/bootstrap/issues/2990877#comment-12719241 but they are complete enough in themselves to help others out who encounter the same issue as me.

My issue was, that after following the steps on https://drupal-bootstrap.org/api/bootstrap/docs%21Sub-Theming.md/group/s... I had no theme-ing/theming when I enabled my subtheme - text was there but no styling.

On working out the missing steps that I wrote up in: https://www.drupal.org/project/bootstrap/issues/2990877#comment-12719241 my sub-theme then worked.

I would therefore now need to make a Pull Request for https://drupal-bootstrap.org/api/bootstrap/docs%21Sub-Theming.md/group/s... so that my suggested additions of the essential steps can be added to this page, after being reviewed by the document owner(s).

Because I would like to make this PR, I have assigned this issue to myself.

Thank you.