Here you go. There's a tiny filmstrip icon above the reply box. Click on it and insert the web address of the video.
Nice work on the pew BTW.
Edited to add that I had to go to the video page on youtube and copy the address from there. Your link clearly takes you to the video page but when I put it in as a video link it wouldn't show up for some reason. this is what I pasted: https://www.youtube.com/watch?v=3GD53wFwREA&feature=youtu.be if that makes any sense at all.