Amended docstring to reflect the actual behaviour of Dataset.map (#6232)

* Amended docstring to reflect the actual behaviour of Dataset.map

* Update

Author: lpilz

xarray/core/dataset.py

@@ -5116,9 +5116,9 @@ def map(
             to transform each DataArray `x` in this dataset into another
             DataArray.
         keep_attrs : bool, optional
-            If True, the dataset's attributes (`attrs`) will be copied from
-            the original object to the new one. If False, the new object will
-            be returned without attributes.
+            If True, both the dataset's and variables' attributes (`attrs`) will be
+            copied from the original objects to the new ones. If False, the new dataset
+            and variables will be returned without copying the attributes.
         args : tuple, optional
             Positional arguments passed on to `func`.
         **kwargs : Any