Added documentation for login related pages

game/lib/interests/interests_page.dart

@@ -5,6 +5,8 @@ import 'package:google_sign_in/google_sign_in.dart';
 import 'package:game/utils/utility_functions.dart';
 import 'package:flutter_svg/flutter_svg.dart';
 
+/// This page allows the user to select their interests. Connection to backend
+/// (creating the user) happens here.
 class InterestsPageWidget extends StatefulWidget {
   InterestsPageWidget(
       {Key? key,

game/lib/register_page/register_page.dart

@@ -4,6 +4,10 @@ import 'package:game/details_page/details_page.dart';
 import 'package:google_sign_in/google_sign_in.dart';
 import 'package:flutter_svg/flutter_svg.dart';
 
+/// If the google-login user is not registered, this page will be displayed.
+/// The user will be asked to select their enrollment type. The user is created
+/// only when they fill all required information (at registerpage -> details_page
+/// -> interests_page).
 class RegisterPageWidget extends StatefulWidget {
   final GoogleSignInAccount? user;
   final String? idToken;