Added hmac.compare_digest to whatsnew
diff --git a/Doc/whatsnew/3.3.rst b/Doc/whatsnew/3.3.rst
index 68ed9c7..38a9f35 100644
--- a/Doc/whatsnew/3.3.rst
+++ b/Doc/whatsnew/3.3.rst
@@ -1023,6 +1023,15 @@
 (Contributed by Giampaolo Rodolà in :issue:`12139`)
 
 
+hmac
+----
+
+A new :func:`~hmac.compare_digest` function has been added to prevent
+side channel attacks on digests through timing analysis.
+
+(Contributed by Nick Coghlan and Christian Heimes in issue:`15061`)
+
+
 imaplib
 -------