add documentation on nat/stun support in chan_sip

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@76755 65c4cc65-6c06-0410-ace0-fbb531ad65f3

CHANGES

@@ -42,6 +42,13 @@ CLI Changes
 
 SIP changes
 -----------
+   * Improved NAT and STUN support.
+      chan_sip now can use port numbers in bindaddr, externip and externhost
+      options, as well as contact a STUN server to detect its external address
+      for the SIP socket. See sip.conf.sample, 'NAT' section.
+   * Added the bindaddr option to gtalk.conf.
+   * Added the ability to specify arguments to the Dial application when using
+     the DUNDi switch in the dialplan.
   * The default SIP useragent= identifier now includes the Asterisk version
   * A new option, match_auth_username in sip.conf changes the matching of incoming requests.
      If set, and the incoming request carries authentication info,