[Docs] Add "About" Heading to README.md (#2260)

Author: blueceiling

README.md

@@ -27,7 +27,7 @@ Easy, fast, and cheap LLM serving for everyone
 - [2023/06] We officially released vLLM! FastChat-vLLM integration has powered [LMSYS Vicuna and Chatbot Arena](https://chat.lmsys.org) since mid-April. Check out our [blog post](https://vllm.ai).
 
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+## About
 vLLM is a fast and easy-to-use library for LLM inference and serving.
 
 vLLM is fast with: