docs: added migration guide for Medusa React (#3066)

* docs: added migration guide for Medusa React

* docs: fixed vale error

www/docs/src/utils/reverseSidebar.js

@@ -0,0 +1,10 @@
+module.exports = function reverseSidebarItems(items) {
+  // Reverse items in categories
+  const result = items.map((item) => {
+    if (item.type === 'category' && item.customProps?.sort === 'desc') {
+      return {...item, items: reverseSidebarItems(item.items)};
+    }
+    return item;
+  });
+  return result;
+}