Start a user-specific variant of the install file command.

nix/configuration/util/install_files/default.nix

@@ -15,8 +15,40 @@ in
 {
   imports = [ ];
 
-  options.me = {
+  options.me.install = {
-    install.file = lib.mkOption {
+    user = lib.mkOption {
+      type = lib.types.attrsOf (
+        lib.types.submodule (
+          { username, config, ... }:
+          {
+            options = {
+              enable = lib.mkOption {
+                type = lib.types.bool;
+                default = true;
+                defaultText = "me.install.file.‹username›.enable";
+                example = false;
+                description = "Whether we want to install files in this user's home directory.";
+              };
+              target_username = lib.mkOption {
+                type = lib.types.str;
+                defaultText = "me.install.file.‹username›.target_username";
+                example = "root";
+                description = "The username for the user whose home directory will contain the file.";
+              };
+            };
+
+            config = {
+              target_username = lib.mkDefault username;
+            };
+          }
+        )
+      );
+
+      defaultText = "me.install.user.‹username›";
+      default = { };
+      # TODO: example
+    };
+    file = lib.mkOption {
       type = lib.types.attrsOf (
         lib.types.submodule (
           { name, config, ... }: