added exercises

Author: mhjensen

doc/LectureNotes/_toc.yml

@@ -54,7 +54,8 @@ parts:
     - file: exercisesweek39.ipynb
     - file: week39.ipynb
     - file: week40.ipynb
-    - file: week41.ipynb            
+    - file: week41.ipynb
+    - file: exercisesweek41.ipynb    
   - caption: Projects
     numbered: false
     chapters: