docs: add QR code option to README

Author: lredoban

README.md

@@ -249,6 +249,11 @@ the `with` parameter.
   Default: `${{ github.token }}`, which gives the action permission to
   deploy to the current repository.
 
+- `qr-code`: Whether to include a QR code in the preview comment for easy mobile access.
+  When enabled, a QR code linking to the preview URL will be displayed in the comment.
+
+  Default: `false`
+
 - **(Advanced)** `action`: Determines what this action will do when it is
   executed. Supported values: `deploy`, `remove`, `none`, `auto`.