markdown show youtube video link

Use markdown :

[![IMAGE ALT TEXT HERE](https://img.youtube.com/vi/YOUTUBE_VIDEO_ID_HERE/0.jpg)](https://www.youtube.com/watch?v=YOUTUBE_VIDEO_ID_HERE)

Use html :

<div align="center">
  <a href="https://www.youtube.com/watch?v=YOUTUBE_VIDEO_ID_HERE"><img src="https://img.youtube.com/vi/YOUTUBE_VIDEO_ID_HERE/0.jpg" alt="IMAGE ALT TEXT"></a>
</div>