fix: typos in readme

Author: dongdongzhaoUP

README.md

@@ -41,8 +41,8 @@ This enables multi-step reasoning, reviewer-style critique, and structured revis
     - [1. Clone the Repository](#1-clone-the-repository)
     - [2. Start MongoDB](#2-start-mongodb)
     - [3. Environment Configuration](#3-environment-configuration)
-    - [4. Custom MCP Backend Orchestration](#4-custom-mcp-backend-orchestration)
-    - [5. Build and Run](#4-build-and-run)
+    - [4. Custom MCP Backend Orchestration](#4-custom-mcp-backend-orchestration-optional-for-local-dev)
+    - [5. Build and Run](#5-build-and-run)
   - [Frontend Extension Build](#frontend-extension-build)
     - [Chrome Extension Development](#chrome-extension-development)
     - [Installing the Development Extension](#installing-the-development-extension)