update readme (bug #3309)

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/v1-0@4974 65c4cc65-6c06-0410-ace0-fbb531ad65f3

diff --git a/doc/README.variables b/doc/README.variables
index b703b54ae42465031a13d9cd13801edbe76e1114..d145a217649d1940a2dc6c64d874a2031734d307 100755 (executable)
--- a/doc/README.variables
+++ b/doc/README.variables
@@ -75,6 +75,9 @@ ${TIMESTAMP}  Current date time in the format: YYYYMMDD-HHMMSS
 ${TXTCIDNAME}  Result of application TXTCIDName
 ${UNIQUEID}    Current call unique identifier
 
+NOTE: Attempting to set any of these "special" variables will not change 
+      their value, but will not display any warning either.
+
 The dial() application sets the following variables:
 
 ${DIALEDPEERNAME} Dialed peer name