docs: Outdated custom embed blocks page

doc/custom_embed_blocks.md

@@ -88,11 +88,17 @@ Future<void> _addEditNote(BuildContext context, {Document? document}) async {
           )
         ],
       ),
-      content: QuillEditor.basic(
+      content: QuillProvider(
+      configurations: QuillConfigurations(
         controller: quillEditorController,
+      ),
+      child: QuillEditor.basic(
+        configurations: const QuillEditorConfigurations(
           readOnly: false,
           ),
         ),
+      ),
+    ),
   );
 
   if (quillEditorController.document.isEmpty()) return;