arp-scan: add page (#1699)

pages/linux/arp-scan.md

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+# arp-scan
+
+> Send ARP packets to hosts (specified as IP addresses or hostnames) to scan the local network.
+
+- Scan the current local network:
+
+`arp-scan --localnet`
+
+- Scan an IP network with a custom bitmask:
+
+`arp-scan {{192.168.1.1}}/{{24}}`
+
+- Scan an IP network within a custom range:
+
+`arp-scan {{127.0.0.0}}-{{127.0.0.31}}`
+
+- Scan an IP network with a custom net mask:
+
+`arp-scan {{10.0.0.0}}:{{255.255.255.0}}`