Add documentation and example for linux tun

docs/configuration/inbound/tun.md

@@ -0,0 +1,78 @@
+!!! error ""
+
+    Linux only
+
+### Structure
+
+```json
+{
+  "inbounds": [
+    {
+      "type": "tun",
+      "tag": "tun-in",
+      
+      "inet4_address": "172.19.0.1/30",
+      "inet6_address": "fdfe:dcba:9876::1/128",
+      "mtu": 1500,
+      "auto_route": true,
+      "hijack_dns": true,
+      
+      "sniff": true,
+      "sniff_override_destination": false,
+      "domain_strategy": "prefer_ipv4"
+    }
+  ]
+}
+```
+
+### Tun Fields
+
+#### inet4_address
+
+==Required==
+
+IPv4 prefix for the tun interface.
+
+#### inet6_address
+
+IPv6 prefix for the tun interface.
+
+#### mtu
+
+The maximum transmission unit.
+
+#### auto_route
+
+Set the default route to the Tun.
+
+!!! error ""
+
+    To avoid traffic loopback, set `route.auto_delect_interface` or `outbound.bind_interface`
+
+#### hijack_dns
+
+Hijack TCP/UDP DNS requests to the built-in DNS adapter.
+
+### Listen Fields
+
+#### sniff
+
+Enable sniffing.
+
+Reads domain names for routing, supports HTTP TLS for TCP, QUIC for UDP.
+
+This does not break zero copy, like splice.
+
+#### sniff_override_destination
+
+Override the connection destination address with the sniffed domain.
+
+If the domain name is invalid (like tor), this will not work.
+
+#### domain_strategy
+
+One of `prefer_ipv4` `prefer_ipv6` `ipv4_only` `ipv6_only`.
+
+If set, the requested domain name will be resolved to IP before routing.
+
+If `sniff_override_destination` is in effect, its value will be taken as a fallback.