Added signature node to QR node output in InvoiceSigner.

Author: Saleh7

src/InvoiceSigner.php

@@ -116,9 +116,12 @@ private function getQRNode(string $QRCode): string
         <cac:Attachment>
             <cbc:EmbeddedDocumentBinaryObject mimeCode=\"text/plain\">$QRCode</cbc:EmbeddedDocumentBinaryObject>
         </cac:Attachment>
-    </cac:AdditionalDocumentReference>";
+    </cac:AdditionalDocumentReference>
+    <cac:Signature>
+        <cbc:ID>urn:oasis:names:specification:ubl:signature:Invoice</cbc:ID>
+        <cbc:SignatureMethod>urn:oasis:names:specification:ubl:dsig:enveloped:xades</cbc:SignatureMethod>
+    </cac:Signature>";
     }
-
     /**
      * Get signed invoice XML.
      *