Update week1.do.txt

Author: mhjensen

doc/src/week1/week1.do.txt

@@ -2,7 +2,7 @@ TITLE: Quantum Computing and Quantum Machine Learning
 AUTHOR: Morten Hjorth-Jensen {copyright, 1999-present|CC BY-NC} at Department of Physics, University of Oslo, Norway
 DATE: January 22, 2025
 
-
+# add material about density matrices and bloch sphere, perhaps in week 2
 
 !split
 ===== Overview of first week, Basic Notions of Quantum Mechanics =====