document Zap dial string options in sample config (bug #4165)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@5576 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/extensions.conf.sample

@@ -51,6 +51,16 @@ CONSOLE=Console/dsp				; Console interface for demo
 IAXINFO=guest					; IAXtel username/password
 ;IAXINFO=myuser:mypass
 TRUNK=Zap/g2					; Trunk interface
+;
+; Note the 'g2' in the TRUNK variable above. It specifies which group (defined
+; in zapata.conf) to dial, i.e. group 2, and how to choose a channel to use in
+; the specified group. The four possible options are:
+;
+; g: select the lowest-numbered non-busy Zap channel (aka. ascending sequential hunt group).
+; G: select the highest-numbered non-busy Zap channel (aka. descending sequential hunt group).
+; r: use a round-robin search, starting at the next highest channel than last time (aka. ascending rotary hunt group).
+; R: use a round-robin search, starting at the next lowest channel than last time (aka. descending rotary hunt group).
+;
 TRUNKMSD=1					; MSD digits to strip (usually 1 or 0)
 ;TRUNK=IAX2/user:pass@provider