There is a significant error in the instructions that prevent the plugin from working. This probably explains why a few of the comments are pointing out that nothing happened for them when restarting Strapi.
The step that says:
Replace the content of your ".src\plugins\wysiwyg\admin\src\components\QuillEditor\index.js" with the following code:
Should instead say:
Replace the content of your ".src\plugins\wysiwyg\admin\src\index.js" with the following code:
Once I made that change, it worked as expected.