vnstat: add page (#4875)

pages/linux/vnstat.md

@@ -0,0 +1,23 @@
+# vnstat
+
+> A console-based network traffic monitor.
+
+- Display traffic summary for all interfaces:
+
+`vnstat`
+
+- Display traffic summary for a specific network interface:
+
+`vnstat -i {{eth0}}`
+
+- Display live stats for a specific network interface:
+
+`vnstat -l -i {{eth0}}`
+
+- Show traffic statistics on an hourly basis for the last 24 hours using a bar graph:
+
+`vnstat -hg`
+
+- Measure and show average traffic for 30 seconds:
+
+`vnstat -tr {{30}}`