Add note about the file as per discussion on:
http://mail-archives.apache.org/mod_mbox/jakarta-jmeter-dev/200502.mbox/%3C25aac9fc0502230646d7271ad@mail.gmail.com%3E

git-svn-id: https://svn.apache.org/repos/asf/jmeter/trunk@1620127 13f79535-47bb-0310-9956-ffa450edef68