Update notes for submitted changes

* apps/app_playback.c: Add 'mix' option to app_playback

a6/8ef6aafda6a00576262a3b33cb11eb1058baff

@@ -0,0 +1,9 @@
+Code-Review+1: Joshua Colp <jcolp@sangoma.com>
+Code-Review+1: Sean Bright <sean@seanbright.com>
+Code-Review+2: George Joseph <gjoseph@digium.com>
+Verified+2: George Joseph <gjoseph@digium.com>
+Submitted-by: George Joseph <gjoseph@digium.com>
+Submitted-at: Thu, 21 Oct 2021 10:47:15 -0500
+Reviewed-on: https://gerrit.asterisk.org/c/asterisk/+/16540
+Project: asterisk
+Branch: refs/heads/16