docs: add demo in README

Author: Djaytan

README.md

@@ -17,6 +17,12 @@ Available in [Docker Hub](https://hub.docker.com/r/djaytan/papermc-server).
 
 </div>
 
+## 💻 Demonstration (12 seconds)
+
+<div align="center">
+  <a href="https://asciinema.org/a/722427?autoplay=1" target="_blank"><img src="https://github.com/Djaytan/docker-papermc-server/blob/main/docs/asciinema/demo.gif" alt="asciicast"></a>
+</div>
+
 ## 📘 Usage
 
 For a quick start, you can run the following command: