config: update debuglevel description + sample conf

sample-lnd.conf

@@ -193,10 +193,10 @@
 
 ; Debug logging level.
 ; Valid levels are {trace, debug, info, warn, error, critical}
-; You may also specify <subsystem>=<level>,<subsystem2>=<level>,... to set
-; log level for individual subsystems.  Use lncli debuglevel --show to list
-; available subsystems.
-; debuglevel=info
+; You may also specify <global-level>,<subsystem>=<level>,<subsystem2>=<level>,... 
+; to set log level for individual subsystems.  Use lncli debuglevel --show to 
+; list available subsystems.
+; debuglevel=debug,PEER=info
 
 ; Write CPU profile to the specified file.
 ; cpuprofile=