docs: Update return statement

Author: tony

libtmux/common.py

@@ -423,7 +423,7 @@ def where(self, attrs: D, first: bool = False) -> t.Union[List[O], O]:
 
         Returns
         -------
-        list
+        list of objects, or one object if ``first=True``
         """
 
         # from https://github.com/serkanyersen/underscore.py