docs: Outdated custom embed blocks page

doc/custom_embed_blocks.md

@@ -88,9 +88,15 @@ Future<void> _addEditNote(BuildContext context, {Document? document}) async {
           )
         ],
       ),
-      content: QuillEditor.basic(
+      content: QuillProvider(
+      configurations: QuillConfigurations(
         controller: quillEditorController,
-        readOnly: false,
+      ),
+      child: QuillEditor.basic(
+        configurations: const QuillEditorConfigurations(
+          readOnly: false,
+          ),
+        ),
       ),
     ),
   );