Merge pull request nus-cs2103-AY2021S1#91 from khor-jingqian/2101-update-ug-dg

Fill in missing contributions for Timetable in UG

Author: khor-jingqian

docs/UserGuide.md

@@ -231,7 +231,7 @@ Example:
 
 ![Find Lessons](./images/find_lessons.png);
 
-### 3.4 Timetable
+### 3.4 Timetable (Nicholas)
 
 #### 3.4.1 Add routine to timetable : `timetable_add_routine`