week 4 course notes update

Author: jding25

_modules/week-04.md

@@ -4,12 +4,14 @@ title: Week 4
 
 Sep 17
 : **Lecture 6**{: .label .label-lecture} Regex
+    : [Note 6](https://ds100.org/course-notes/regex/regex.html)
 : **Discussion 3**{: .label .label-disc } [Pandas II, EDA](https://drive.google.com/file/d/1_Vdx0mSN1tIvcS_Ggh8EHdJtm6-qnG02/view?usp=sharing){:target="_blank"}
     : [Mini-Lecture](https://www.youtube.com/watch?v=9jFqjbPLThc&list=PLQCcNQgUcDfplNp0itu2QqVjoDE9u5iow&index=3)
 
 
 Sep 19
 : **Lecture 7**{: .label .label-lecture} Visualization I
+    : [Note 7](https://ds100.org/course-notes/visualization_1/visualization_1.html)
 
 
 Sep 20