add comments about dhcp listen section

raddb/sites-available/dhcp

@@ -94,17 +94,30 @@ server dhcp {
 # The other only solution is to update FreeRADIUS to use BPF sockets.
 #
 listen {
+	#  This is a dhcp socket.
+	type = dhcp
+
+	#  IP address to listen on. Will usually be the IP of the
+	#  interface, or 0.0.0.0
 	ipaddr = 127.0.0.1
+
+	#  The port should be 67 for a production network. Don't set
+	#  it to 67 on a production network unless you really know
+	#  what you're doing. Even if nothing is configured below, the
+	#  server may still NAK legitimate responses from clients.
 	port = 6700
-	type = dhcp
+
+	#  Interface name we are listening on. See comments above.
 #	interface = lo0
 
 	# The DHCP server defaults to allowing broadcast packets.
 	# Set this to "no" only when the server receives *all* packets
 	# from a relay agent.  i.e. when *no* clients are on the same
 	# LAN as the DHCP server.
 	#
-	# It's set to "no" here for testing.
+	# It's set to "no" here for testing. It will usually want to
+	# be "yes" in production, unless you are only dealing with
+	# relayed packets.
 	broadcast = no
 
 	# On Linux if you're running the server as non-root, you