add documentation for peer-specific 'outboundproxy' setting

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.2@36253 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/sip.conf.sample

@@ -308,6 +308,7 @@ srvlookup=yes			; Enable DNS SRV lookups on outbound calls
 ;                             rtptimeout
 ;                             rtpholdtimeout
 ;                             sendrpid
+;                             outboundproxy
 
 ;[sip_proxy]
 ; For incoming calls only. Example: FWD (Free World Dialup)
@@ -326,6 +327,7 @@ srvlookup=yes			; Enable DNS SRV lookups on outbound calls
 ;host=box.provider.com
 ;usereqphone=yes			; This provider requires ";user=phone" on URI
 ;call-limit=5				; permit only 5 simultaneous outgoing calls to this peer
+;outboundproxy=proxy.provider.domain	; send outbound signaling to this proxy, not directly to the peer
 
 ;------------------------------------------------------------------------------
 ; Definitions of locally connected SIP phones