Add additional link to best practices document per jsmith.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.2@247507 65c4cc65-6c06-0410-ace0-fbb531ad65f3

README-SERIOUSLY.bestpractices.txt

@@ -33,6 +33,9 @@ security are listed below.
 * Seven Steps to Better SIP Security:
         http://blogs.digium.com/2009/03/28/sip-security/
 
+* Asterisk VoIP Security (webinar):
+        http://www.asterisk.org/security/webinar/
+
 
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