nixos/clash: add option descriptions

nixos/modules/services/clash.nix

@@ -7,21 +7,34 @@
   cfg = config.services.clash;
 in {
   options.services.clash = {
-    enable = lib.mkEnableOption "Whether to enable Clash, A rule-based proxy in Go";
+    enable = lib.mkEnableOption "Whether to enable Clash, A rule-based proxy in Go.";
     package = lib.mkPackageOption pkgs "clash" {};
-
-    # TODO
-    webui = lib.mkOption {
-      default = null;
-      type = lib.types.nullOr lib.types.path;
-    };
     configFile = lib.mkOption {
       default = null;
       type = lib.types.nullOr lib.types.path;
+      description = "Configuration file to use.";
+    };
+    webui = lib.mkOption {
+      default = null;
+      type = lib.types.nullOr lib.types.path;
+      description = ''
+        Local web interface to use.
+
+        You can also use the following website, just in case:
+        - metacubexd:
+          - http://d.metacubex.one
+          - https://metacubex.github.io/metacubexd
+          - https://metacubexd.pages.dev
+        - yacd:
+          - https://yacd.haishan.me
+        - clash-dashboard (buggy):
+          - https://clash.razord.top
+      '';
     };
     extraOpts = lib.mkOption {
       default = null;
       type = lib.types.nullOr lib.types.string;
+      description = "Extra command line options to use.";
     };
   };
 
@@ -52,8 +65,8 @@ in {
         ExecStart = builtins.replaceStrings ["\n"] [" "] ''
           ${lib.getExe cfg.package}
           -d /etc/clash
-          ${lib.optionalString (cfg.webui != null) "-ext-ui ${cfg.webui}"}
           ${lib.optionalString (cfg.configFile != null) "-f \${CREDENTIALS_DIRECTORY}/configuration"}
+          ${lib.optionalString (cfg.webui != null) "-ext-ui ${cfg.webui}"}
           ${lib.optionalString (cfg.extraOpts != null) cfg.extraOpts}
         '';