Fix reference to README files

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@13549 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/sip.conf.sample

@@ -205,7 +205,7 @@ srvlookup=yes			; Enable DNS SRV lookups on outbound calls
 
 ;----------------------------------------- REALTIME SUPPORT ------------------------
 ; For additional information on ARA, the Asterisk Realtime Architecture,
-; please read README.realtime and README.extconfig in the /doc directory of the
+; please read realtime.txt and extconfig.txt in the /doc directory of the
 ; source code.
 ;
 ;rtcachefriends=yes		; Cache realtime friends by adding them to the internal list