DOC-3309: add note about mediaembed in js code for demo.

Author: kemister85

modules/ROOT/examples/live-demos/basic-example/index.js

@@ -4,7 +4,9 @@ tinymce.init({
   plugins: [
     'advlist', 'autolink', 'lists', 'link', 'image', 'charmap', 'preview',
     'anchor', 'searchreplace', 'visualblocks', 'code', 'fullscreen',
-    'insertdatetime', 'media', 'table', 'help', 'wordcount', 'mediaembed'
+    'insertdatetime', 'media', 'table', 'help', 'wordcount',
+    /* Premium plugins for demo purposes only */
+    'mediaembed',
   ],
   toolbar: 'undo redo | blocks | ' +
   'bold italic backcolor | alignleft aligncenter ' +