Update README.md (#976)

### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

### Type of change

- [x] Documentation Update

README.md

@@ -24,6 +24,25 @@
   </a>
 </p>
 
+<details open>
+<summary></b>📕 Table of Contents</b></summary>
+
+- [💡 What is RAGFlow?](#what-is-ragflow)
+- [🎮 Demo](#demo)
+- [📌 Latest Updates](#latest-updates)
+- [🌟 Key Features](#key-features)
+- [🔎 System Architecture](#system-architecture)
+- [🎬 Get Started](#get-started)
+- [🔧 Configurations](#configurations)
+- [🛠️ Build from source](#build-from-source)
+- [🛠️ Launch service from source](#launch-service-from-source)
+- [📚 Documentation](#documentation)
+- [📜 Roadmap](#roadmap)
+- [🏄 Community](#community)
+- [🙌 Contributing](#contributing)
+
+</details>
+
 ## 💡 What is RAGFlow?
 
 [RAGFlow](https://ragflow.io/) is an open-source RAG (Retrieval-Augmented Generation) engine based on deep document understanding. It offers a streamlined RAG workflow for businesses of any scale, combining LLM (Large Language Models) to provide truthful question-answering capabilities, backed by well-founded citations from various complex formatted data.