feat(flake): add apps

apps/default.nix

@@ -0,0 +1,8 @@
+# Custom apps, that can be defined similarly to ones from nixpkgs
+# You can build them using 'nix run .#example'
+
+{ pkgs ? (import ../nixpkgs.nix) { }
+, ...
+}: {
+  # example = import ./example { inherit pkgs; };
+}

flake.nix

@@ -81,7 +81,9 @@
       );
 
       # Apps (`nix run`)
-      apps = { };
+      apps = forEachPkgs (pkgs:
+        import ./apps { inherit pkgs; }
+      );
 
       # Dev Shells (`nix develop`)
       devShells = forEachPkgs (pkgs: