added vue comment

#1635

Author: adumesny

demo/vue3js.html

@@ -34,6 +34,7 @@ <h1>How to integrate GridStack.js with Vue.js</h1>
       createApp({
         data() {
           return {
+            // grid: undefined, // <-- don't do that. see https://github.com/gridstack/gridstack.js/issues/1635
             count: 0,
             info: "",
           };