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.

Doc/library/hashlib.rst

@@ -33,6 +33,8 @@ digests.  The modern term is secure hash.
    also" section at the end.
 
 
+.. _hash-algorithms:
+
 Hash algorithms
 ---------------
 
@@ -63,7 +65,7 @@ Constructors for hash algorithms that are always present in this module are
 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'``::

Doc/whatsnew/3.4.rst

@@ -112,7 +112,7 @@ Significantly Improved Library Modules:
 * :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 @@ hashlib
 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
 ----