release.nix: Build the demo rootfs

As thus rootfs is universal, building it will allow end-users to
directly be able to run a somewhat usable system on their devices, even
if they are unable to bootstrap themselves one.

Furthermore, this ensures that the requirements are built and do
continue building on aarch64-linux.

release.nix

@@ -79,6 +79,21 @@ let
     }
   ;
 
+  specialConfig = {name, buildingForSystem, system}: {
+    special = true;
+    inherit name;
+    config = {
+      mobile.device.info = {};
+      mobile.system.type = "none";
+      mobile.hardware.soc = {
+        x86_64-linux = "generic-x86_64";
+        aarch64-linux = "generic-aarch64";
+        armv7l-linux = "generic-armv7l";
+      }.${buildingForSystem};
+      nixpkgs.localSystem = knownSystems.${system};
+    };
+  };
+
   # Given a system builds run on, this will return a set of further systems
   # this builds in, either native or cross.
   # The values are `overlayForEval` applied for the pair local/cross systems.
@@ -89,19 +104,7 @@ let
         # "device" name for the eval *and* key used for the set.
         name = if system == buildingForSystem then buildingForSystem else "${buildingForSystem}-cross";
         # "device" eval for our dummy device.
-        eval = evalFor {
-          special = true;
-          inherit name;
-          config = {
-            mobile.system.type = "none";
-            mobile.hardware.soc = {
-              x86_64-linux = "generic-x86_64";
-              aarch64-linux = "generic-aarch64";
-              armv7l-linux = "generic-armv7l";
-            }.${buildingForSystem};
-            nixpkgs.localSystem = knownSystems.${system};
-          };
-        };
+        eval = evalFor (specialConfig {inherit name buildingForSystem system;});
         overlay = overlayForEval eval;
       in {
         inherit name;
@@ -119,9 +122,21 @@ let
       } device).build.default
     )
   );
+
+  examples-demo =
+    let
+      device = (specialConfig {
+        name = "aarch64-linux";
+        buildingForSystem = "aarch64-linux";
+        system = "aarch64-linux";
+      });
+    in
+    import ./examples/demo { inherit device; };
+  examples-demo-rootfs = examples-demo.build.rootfs;
 in
 {
   inherit device;
+  inherit examples-demo-rootfs;
 
   # Overlays build native, and cross, according to shouldEvalOn
   overlay = lib.genAttrs systems (system:
@@ -141,6 +156,7 @@ in
       ++ lib.optionals (hasSystem "aarch64-linux") [
         device.asus-z00t.aarch64-linux               # Android
         device.asus-dumo.aarch64-linux               # Depthcharge
+        examples-demo-rootfs 
       ];
   in
   releaseTools.aggregate {