Add log and dns documentation

docs/configuration/dns/server.md

@@ -0,0 +1,58 @@
+### Structure
+
+```json
+{
+  "dns": {
+    "servers": [
+      {
+        "tag": "google",
+        "address": "tls://dns.google",
+        "address_resolver": "local",
+        "address_strategy": "prefer_ipv4",
+        "detour": "direct"
+      }
+    ]
+  }
+}
+
+```
+
+### Fields
+
+#### tag
+
+The tag of the dns server.
+
+#### address
+
+The address of the dns server.
+
+| Protocol | Format                      |
+|----------|-----------------------------|
+| `System` | `local`                     |
+| `TCP`    | `tcp://1.0.0.1`             |
+| `UDP`    | `8.8.8.8` `udp://8.8.4.4`   |
+| `TLS`    | `tls://dns.google`          |
+| `HTTPS`  | `https://1.1.1.1/dns-query` |
+
+!!! warning ""
+
+    To ensure that system DNS is in effect, rather than go's built-in default resolver, enable CGO at compile time.
+
+#### address_resolver
+
+Tag of a another server to resolve the domain name in the address.
+
+#### address_strategy
+
+The domain strategy for resolving the domain name in the address.
+
+One of `prefer_ipv4` `prefer_ipv6` `ipv4_only` `ipv6_only`.
+
+`dns.strategy` will be used if `address_strategy` is empty.
+
+#### detour
+
+Tag of an outbound for connecting to the dns server.
+
+Requests will be sent directly if the empty.