Make sure we give a little warning about the echotraining option

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@42324 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/zapata.conf.sample

@@ -352,6 +352,11 @@ echocancelwhenbridged=yes
 ; closer idea of the actual echo.  Value may be "yes", "no", or a number of
 ; milliseconds to delay before training (default = 400)
 ;
+; WARNING:  In some cases this option can make echo worse!  If you are
+; trying to debug an echo problem, it is worth checking to see if your echo
+; is better with the option set to yes or no.  Use whatever setting gives
+; the best results.
+;
 ; Note that these parameters do not apply to hardware echo cancellers.
 ;
 ;echotraining=yes