bpo-24310: Document IDLE settings dialog font tab sample (GH-12007)

diff --git a/Lib/idlelib/NEWS.txt b/Lib/idlelib/NEWS.txt
index 5d30fb3..715b013 100644
--- a/Lib/idlelib/NEWS.txt
+++ b/Lib/idlelib/NEWS.txt
@@ -3,6 +3,8 @@
 ======================================
 
 
+bpo-24310: Document settings dialog font tab sample.
+
 bpo-35689: Add docstrings and tests for colorizer.
 
 bpo-35833: Revise IDLE doc for control codes sent to Shell.