add video (#732)

README.md

@@ -25,6 +25,7 @@
 
 ## Table of Contents
 <ul>
+ <li><a href="#Why-Colossal-AI">Why Colossal-AI</a> </li>
  <li><a href="#Features">Features</a> </li>
  <li>
    <a href="#Demo">Demo</a> 
@@ -55,6 +56,17 @@
  <li><a href="#Cite-Us">Cite Us</a></li>
 </ul>
 
+## Why Colossal-AI
+<div align="center">
+   <a href="https://youtu.be/KnXSfjqkKN0">
+   <img src="https://raw.githubusercontent.com/hpcaitech/public_assets/main/colossalai/img/JamesDemmel_Colossal-AI.png" width="600" />
+   </a>
+
+   Prof. James Demmel (UC Berkeley): Colossal-AI makes distributed training efficient, easy and scalable.
+</div>
+
+<p align="right">(<a href="#top">back to top</a>)</p>
+
 ## Features
 
 Colossal-AI provides a collection of parallel training components for you. We aim to support you to write your