added link to describing videos

slides/assessment.html

@@ -358,6 +358,7 @@ More commonly available today than ever
 Let's try it: Form groups and open [YouDescribe](https://youdescribe.org/);
 ([post a link to your video](TBD))
 
+If you want to know more: [describing educational videos](https://dcmp.org/learn/descriptionkey)
 ---
 # POUR: Perceivable: Guidelines 1.1-1.4