bpo-37955: correct mock.patch docs with respect to the returned type (GH-15521)

diff --git a/Doc/library/unittest.mock.rst b/Doc/library/unittest.mock.rst
index 8394304..515bdd0 100644
--- a/Doc/library/unittest.mock.rst
+++ b/Doc/library/unittest.mock.rst
@@ -1401,7 +1401,8 @@
     "as"; very useful if :func:`patch` is creating a mock object for you.
 
     :func:`patch` takes arbitrary keyword arguments. These will be passed to
-    the :class:`Mock` (or *new_callable*) on construction.
+    :class:`AsyncMock` if the patched object is asynchronous, to
+    :class:`MagicMock` otherwise or to *new_callable* if specified.
 
     ``patch.dict(...)``, ``patch.multiple(...)`` and ``patch.object(...)`` are
     available for alternate use-cases.