Add configuration for log, ttl, server-name

cache cname.

etc/smartdns/smartdns.conf

@@ -1,3 +1,9 @@
+# dns server name, defaut is host name
+# server-name, 
+# example:
+#   server-name smartdns
+#
+
 # dns server bind ip and port, default dns server port is 53.
 # bind [IP]:port, 
 # example: 
@@ -11,9 +17,22 @@ bind [::]:53
 #   0: for no cache
 cache-size 512
 
+# ttl for all resource record
+# rr-ttl: ttl for all record
+# rr-ttl-min: minimum ttl for resource record
+# rr-ttl-max: maximum ttl for resource record
+# example:
+# rr-ttl 300
+# rr-ttl-min 60
+# rr-ttl-max 86400
+
 # set log level
-# loglevel [level], level=error, warn, info, debug
-loglevel error
+# log-level [level], level=error, warn, info, debug
+# log-size k,m,g
+log-level error
+# log-file /var/log/smartdns.log
+# log-size 128k
+# log-num 2
 
 # remote udp dns server list
 # server [IP]:[PORT], default port is 53