nslookup: add page (#1174)

Non interactive use of nslookup on *nix-like systems: https://linux.die.net/man/1/nslookup

pages/common/nslookup.md

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+# nslookup
+
+> Query name server(s) for various domain records.
+
+- Query your system's default name server for an IP address (A record) of the domain:
+
+`nslookup {{example.com}}`
+
+- Query a given name server for a NS record of the domain:
+
+`nslookup -type=NS {{example.com}} {{8.8.8.8}}`
+
+- Query for a reverse lookup (PTR record) of an IP address:
+
+`nslookup -type=PTR {{54.240.162.118}}`
+
+- Query for ANY available records using TCP protocol:
+
+`nslookup -vc -type=ANY {{example.com}} `
+
+- Query a given name server for the whole zone file (zone transfer) of the domain using TCP protocol:
+
+`nslookup -vc -type=AXFR {{example.com}} {{name_server}}`
+
+- Query for a mail server (MX record) of the domain, showing details of the transaction:
+
+`nslookup -type=MX -debug {{example.com}}`
+
+- Query a given name server on a specific port number for a TXT record of the domain:
+
+`nslookup -port={{port_number}} -type=TXT {{example.com}} {{name_server}}`