Declare required fields in the documentation

docs/configuration/dns/index.md

@@ -6,7 +6,7 @@
     "servers": [],
     "rules": [],
     "final": "",
-    "strategy": "prefer_ipv6",
+    "strategy": "",
     "disable_cache": false,
     "disable_expire": false
   }
@@ -23,7 +23,9 @@
 
 #### final
 
-Default dns server tag. the first server will be used if empty.
+Default dns server tag.
+
+The first server will be used if empty.
 
 #### strategy
 

docs/configuration/dns/rule.md

@@ -140,4 +140,6 @@ Included default rules.
 
 #### server
 
+==Required==
+
 Tag of the target dns server.

docs/configuration/dns/server.md

@@ -25,6 +25,8 @@ The tag of the dns server.
 
 #### address
 
+==Required==
+
 The address of the dns server.
 
 | Protocol | Format                      |
@@ -41,6 +43,8 @@ The address of the dns server.
 
 #### address_resolver
 
+==Required if address contains domain==
+
 Tag of a another server to resolve the domain name in the address.
 
 #### address_strategy
@@ -55,4 +59,4 @@ One of `prefer_ipv4` `prefer_ipv6` `ipv4_only` `ipv6_only`.
 
 Tag of an outbound for connecting to the dns server.
 
-Requests will be sent directly if the empty.
+Default outbound will be used if empty.