Issue #3363419 by chris matthews, dydave: Updated module description and install message.

https://www.drupal.org/project/block_class/issues/3363419

Updated module description and install message.

Normalized module's composer.json file with package ergebnis/composer-normalize.

Rolled in merge request patch from:
https://www.drupal.org/project/block_class/issues/3363419#comment-15082594

based on the work from @ChrisMatthews.