update docs

README.md

@@ -24,7 +24,9 @@ GROWI
 [![devDependencies Status](https://david-dm.org/weseek/growi/dev-status.svg)](https://david-dm.org/weseek/growi?type=dev)
 [![docker pulls](https://img.shields.io/docker/pulls/weseek/growi.svg)](https://hub.docker.com/r/weseek/growi/)
 
-![sample image](https://user-images.githubusercontent.com/42988650/70600974-6b29cc80-1c34-11ea-94ef-33c39c6a00dc.gif)
+| demonstration |
+| :-: |
+|![sample image](https://user-images.githubusercontent.com/42988650/70600974-6b29cc80-1c34-11ea-94ef-33c39c6a00dc.gif)|
 
 - [Features](#features)
 - [Quick Start for Production](#quick-start-for-production)