Include sha3 addition in hashlib section of whatsnew.

And link to it from the summary, and link to the Hash Algorithms
section of hashlib from the linked description.
diff --git a/Doc/library/hashlib.rst b/Doc/library/hashlib.rst
index b1daba1..ee99178 100644
--- a/Doc/library/hashlib.rst
+++ b/Doc/library/hashlib.rst
@@ -33,6 +33,8 @@
    also" section at the end.
 
 
+.. _hash-algorithms:
+
 Hash algorithms
 ---------------
 
@@ -63,7 +65,7 @@
 the OpenSSL library that Python uses on your platform.
 
    .. versionchanged:: 3.4
-      Add sha3 family of hash algorithms.
+      Added sha3 family of hash algorithms.
 
 For example, to obtain the digest of the byte string ``b'Nobody inspects the
 spammish repetition'``::
diff --git a/Doc/whatsnew/3.4.rst b/Doc/whatsnew/3.4.rst
index 9f84602..fb1721a 100644
--- a/Doc/whatsnew/3.4.rst
+++ b/Doc/whatsnew/3.4.rst
@@ -112,7 +112,7 @@
 * :ref:`Single-dispatch generic functions <whatsnew-singledispatch>` in
   :mod:`functools` (:pep:`443`)
 * New :mod:`pickle` protocol 4 (:pep:`3154`)
-* SHA-3 (Keccak) support for :mod:`hashlib`.
+* :ref:`SHA-3 (Keccak) support <whatsnew-sha3>` for :mod:`hashlib`.
 * TLSv1.1 and TLSv1.2 support for :mod:`ssl`.
 * :mod:`multiprocessing` now has option to avoid using :func:`os.fork`
   on Unix (:issue:`8713`).
@@ -575,6 +575,12 @@
 New :func:`hashlib.pbkdf2_hmac` function.
 (Contributed by Christian Heimes in :issue:`18582`)
 
+.. _whatsnew-sha3:
+
+New :ref:`hash algorithms <hash-algorithms>` ``sah3_224()``, ``sha3_256()``,
+``sha3_384()``, and ``sha3_512()``.  (Contributed by Christian Heimes in
+:issue:`16113`.)
+
 
 html
 ----