Add @modules to docs for using Quill modules (e.g. keyboard module to override tab behavior)

[yutsi]

I discovered that using @modules like this lets you use Quill modules:

<Ql.editor
        @modules={{this.quillModules}}
      />

This allows you to override the default tab behavior.

get quillModules() {
    return {
      keyboard: {
        bindings: {
          // Override tab key to allow normal browser behavior
          tab: {
            key: 9, // Tab key code
            handler: function(range, context) {
              // Return true to allow default browser behavior
              return true;
            }
          }
        }
      }
    };
  }

[lindyhopchris]

Thanks, any chance you could do a PR?