Started network monitoring docu

docs/home-network/admin/monitoring.md

@@ -0,0 +1,14 @@
+# Network monitoring
+
+Discover all devices connected to the local network:
+
+```bash
+#!/bin/bash
+subnet="192.168.0"
+for suffix in $(seq 101 199); do
+    ip_address="$subnet.$suffix"
+    # Only wait 1 second for each response: ping should only take a few
+    # milliseconds on LAN.
+    ping -c 1 -W 1 $ip_address | grep "64 bytes from $ip_address" | awk '{ print $4 }' | sed s/://
+done
+```