[fix] Update README

README.md

@@ -2,6 +2,15 @@
 
 Cobalt is a demo app for hybrid search with vector and surface search using [Ruri](https://huggingface.co/cl-nagoya/ruri-large), [BM25](https://github.com/dorianbrown/rank_bm25) and [Voyager](https://spotify.github.io/voyager/). The name cobalt is derived from the word 瑠璃 (Ruri), which refers to cobalt glass.
 
+## Demo
+This demo app is made by Gradio.
+
+```bash
+gradio app.py
+```
+
+![](./materials/cobalt-gradio-demo.png)
+
 ## Usage
 
 ```python