chore(docs): update TOC

Author: Haruma-K

README.md

@@ -36,7 +36,6 @@ Hierarchical debug menu system for Unity that makes it easy to create intuitive
   - [Workflow in multiple scenes](#workflow-in-multiple-scenes)
   - [Exclude from the release builds](#exclude-from-the-release-builds)
   - [Custom Cells](#custom-cells)
-  - [Extending Built-in Cell Prefabs](#extending-built-in-cell-prefabs)
 - [Advanced Usage](#advanced-usage)
   - [Use async methods instead of coroutines](#use-async-methods-instead-of-coroutines)
   - [Hide Backdrop](#hide-backdrop)
@@ -46,6 +45,7 @@ Hierarchical debug menu system for Unity that makes it easy to create intuitive
   - [Change the min/max size of the debug menu](#change-the-minmax-size-of-the-debug-menu)
   - [Customize the look](#customize-the-look)
   - [Pop multiple screens at once](#pop-multiple-screens-at-once)
+  - [Extending Built-in Cell Prefabs](#extending-built-in-cell-prefabs)
 - [Extension Packages](#extension-packages)
   - [Display the system information of Unity](#display-the-system-information-of-unity)
   - [In-game Debug Console](#in-game-debug-console)