_slides: Clarify portfolio video requirements

_slides/about/introduction/grading.md

@@ -8,13 +8,13 @@ All submitted work in this course is graded on a **Satisfactory (S)** or **Not y
 4.0
 : **S** on all 3 projects.
 : **S** on all 6 checkpoints.
-: **S** on the portfolio.
+: **S** on all 6 portfolio videos.
 : **E** (exemplary) on the research project.
 
 3.0
 : **S** on all 3 projects.
 : **S** on 4 checkpoints.
-: **S** on the portfolio.
+: **S** on 3 portfolio videos.
 : No research project required.
 
 2.0