Add extraHosts option.

modules/environment/networking.nix

@@ -4,11 +4,26 @@
 
 with lib;
 
+let
+  cfg = config.networking;
+in
+
 {
 
   ###### interface
 
-  options = { };
+  options = {
+
+    networking.extraHosts = lib.mkOption {
+      type = types.lines;
+      default = "";
+      example = "192.168.0.1 lanlocalhost";
+      description = lib.mdDoc ''
+        Additional verbatim entries to be appended to {file}`/etc/hosts`.
+      '';
+    };
+
+  };
 
 
   ###### implementation
@@ -26,6 +41,7 @@ with lib;
       hosts.text = ''
         127.0.0.1 localhost
         ::1 localhost
+        ${cfg.extraHosts}
       '';
 
       "resolv.conf".text = ''