Refactor tag to tutorial group in dg

docs/DeveloperGuide.md

@@ -161,7 +161,7 @@ The `Model` component,
 * stores a `UserPref` object that represents the user’s preferences. This is exposed to the outside as a `ReadOnlyUserPref` objects.
 * does not depend on any of the other three components (as the `Model` represents data entities of the domain, they should make sense on their own without depending on other components)
 
-<div markdown="span" class="alert alert-info">:information_source: **Note:** An alternative (arguably, a more OOP) model is given below. It has a `Tag` list in the `AddressBook`, which `Student` references. This allows `AddressBook` to only require one `Tag` object per unique tag, instead of each `Student` needing their own `Tag` objects.<br>
+<div markdown="span" class="alert alert-info">:information_source: **Note:** An alternative (arguably, a more OOP) model is given below. It has a `TutorialGroup` list in the `AddressBook`, which `Student` references. This allows `AddressBook` to only require one `TutorialGroup` object per unique tutorial group, instead of each `Student` needing their own `TutorialGroup` objects.<br>
 
 <img src="images/BetterModelClassDiagram.png" width="450" />