Add docstring for _shorten_with_ellipsis method

tgtg_scanner/notifiers/telegram.py

@@ -533,4 +533,5 @@ def __repr__(self) -> str:
 
     @staticmethod
     def _shorten_with_ellipsis(text: str, length: int = MAX_BUTTON_TEXT_LENGTH) -> str:
+        """Shorten text to length and add ellipsis in the middle"""
         return text if len(text) <= length else text[: (length - 3) // 2] + "..." + text[-(length - 3) // 2 :]