Docstring of expand_dims to reflect that axis can be a tuple

Author: oleksandr-pavlyk

dpctl/tensor/_manipulation_functions.py

@@ -127,8 +127,10 @@ def expand_dims(X, axis):
     of size one at the position specified by axis.
 
     Args:
-        x (usm_ndarray): input array
-        axis (int):  axis position (zero-based). If `x` has rank
+        x (usm_ndarray):
+            input array
+        axis (Union[int, Tuple[int]]):
+            axis position in the expanded axes (zero-based). If `x` has rank
             (i.e, number of dimensions) `N`, a valid `axis` must reside
             in the closed-interval `[-N-1, N]`. If provided a negative
             `axis`, the `axis` position at which to insert a singleton