Fix substitution form again and add comment field

aleksis/apps/chronos/forms.py

@@ -11,7 +11,7 @@ class LessonSubstitutionForm(forms.ModelForm):
 
     class Meta:
         model = LessonSubstitution
-        fields = ["subject", "teachers", "room", "cancelled"]
+        fields = ["subject", "teachers", "room", "cancelled", "comment"]
         widgets = {
             "teachers": ModelSelect2MultipleWidget(
                 search_fields=[