added digital clock demo

Author: sumn2u

en/beginner-projects/digital-clock.md

@@ -20,4 +20,12 @@ A live digital clock that shows the current time in hours, minutes, and seconds.
 ## Bonus Challenge
 Add different time zones or a stopwatch feature.
 
-
+## Live Demo
+<div align="center">
+<iframe src="https://codesandbox.io/embed/wzw6sw?view=preview"
+     style="width:100%; height: 500px; border:0; border-radius: 4px; overflow:hidden;"
+     title="interactive-drum-kit"
+     allow="accelerometer; ambient-light-sensor; camera; encrypted-media; geolocation; gyroscope; hid; microphone; midi; payment; usb; vr; xr-spatial-tracking"
+     sandbox="allow-forms allow-modals allow-popups allow-presentation allow-same-origin allow-scripts"
+   ></iframe>
+   </div>