Add demo link

Author: junjizhi

README.md

@@ -3,6 +3,9 @@
 ## Introduction
 A simple timeline component similar to [Ant Timeline](https://www.antdv.com/components/timeline/) based on [Bootstrap-Vue](https://bootstrap-vue.org/).
 
+## Demo
+[Codesandbox](https://codesandbox.io/s/sad-edison-8r7mh)
+
 ## Screenshots
 <img width="629" alt="image" src="https://user-images.githubusercontent.com/2715151/121779292-eab99400-cb68-11eb-8a2f-02a5ea3d2bf1.png">
 
@@ -133,4 +136,4 @@ yarn doc src/bootstrap-vue-timeline.vue
 
 ## License
 
-Released under the MIT [License](./LICENSE). Copyright (c) Bootstrap-vue-timeline.
+Released under the MIT [License](./LICENSE). Copyright (c) Bootstrap-vue-timeline.