docs: update README

Author: shiqimei

.vscode/extensions.json

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+{
+  "recommendations": [
+    "JipitiAI.askcodebase"
+  ]
+}

README.md

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 # CodeIndex
-High Performance Codebase Index Engine for AI.
+
+CodeIndex is a local-first high performance codebase index engine designed for AI. It helps your LLM understanding the structure and semantics of a codebase.
+
+## Features
+
+- **🔐 Privacy first:** All data is stored locally on your machine.
+- **🚀 High performance:** Indexing a middle codebase takes less than 1 second.
+- **🤖 AI ready:** The index is designed for AI, which means it's easy to provide codebase context to your LLM.
+- **⚙️ Configurable:** The index is designed to be configurable. You can customize the engine to fit your needs.
+
+## Acknowledgement
+
+1. [Sweep AI](https://github.com/sweepai/sweep) Sweep: AI-powered Junior Developer for small features and bug fixes.
+2. [SourceGraph](https://github.com/sourcegraph/sourcegraph) Code AI platform with Code Search & Cody
+3. [LLamaIndex](https://github.com/jerryjliu/llama_index) LlamaIndex (GPT Index) is a data framework for your LLM applications