added example for node hook

etc/example.conf

@@ -40,6 +40,17 @@ nodes = {
 		type = "socket",			# For a list of available node-types run: 'villas-node -h'
 		vectorize = 30,				# Receive and sent 30 samples per message (combining).
 		samplelen = 10				# The maximum number of samples this node can receive
+		
+		hooks = (
+			{
+				type = "stats",
+				
+				warmup = 100,		# The first 100 samples are used to estimate bounds for the histograms
+				format = "human",	# One of: human, json, matlab
+				bucket = 30,		# The number of buckets for the histograms
+				verbose = true		# Plot histograms during shutdown
+			}
+		),
 
 	### The following settings are specific to the socket node-type!! ###