Added comment

src/kleinanzeigen_bot/extract.py

@@ -285,6 +285,7 @@ async def _extract_category_from_ad_page(self) -> str:
  async def _extract_special_attributes_from_ad_page(self) -> dict[str, Any]:
  """
  Extracts the special attributes from an ad page.
+ If no items are available then special_attributes is empty
 
  :return: a dictionary (possibly empty) where the keys are the attribute names, mapped to their values
  """