add comment

fet2020/tasks/models.py

@@ -130,6 +130,7 @@ class Document(models.Model):
         verbose_name_plural = "Dokumente"
 
         constraints = [
+            # TODO: include lower/upper case - when Django 4.0, then go for it.
             UniqueConstraint(
                 fields=["title", "date", "task"], name="unique_task_document"
             ),