studiou-wc-product-cat-manage: add directory structure file

studiou-wc-product-cat-manage/directory-structure.txt

@@ -0,0 +1,15 @@
+studiou-wc-product-cat-manage/
+├── assets/
+│   ├── css/
+│   │   └── admin.css
+│   └── js/
+│       └── admin.js
+├── includes/
+│   ├── class-studiou-wc-product-cat-manage-db.php
+│   ├── class-studiou-wc-product-cat-manage-export.php
+│   └── class-studiou-wc-product-cat-manage-import.php
+├── views/
+│   ├── import.php
+│   └── export.php
+├── readme.md
+└── studiou-wc-product-cat-manage.php