DOC: In `reduce`, refer to `accumulate` (GH-7930)

diff --git a/Doc/library/functools.rst b/Doc/library/functools.rst
index d0e3c7b..5e278f9 100644
--- a/Doc/library/functools.rst
+++ b/Doc/library/functools.rst
@@ -263,6 +263,8 @@
               value = function(value, element)
           return value
 
+   See :func:`itertools.accumulate` for an iterator that yields all intermediate
+   values.
 
 .. decorator:: singledispatch