add a minimal flake exapmle

prezentace.md

@@ -51,4 +51,39 @@ nix why-depends
 # Jak pouzit flakes na system configuraci?
 * Flake je jen cast zbytek je v normalnich nix filech
 * Zbytek konfigurace bere inputy z flaky.
-* Neprijdeme o nic jen mame lock file a moznost flake  jako inputu
+* Neprijdeme o nic jen mame lock file a moznost flake  jako inputu
+---
+# Flake example
+```
+{
+  description = "NixOS configuration";
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    home-manager.url = "github:nix-community/home-manager";
+    home-manager.inputs.nixpkgs.follows = "nixpkgs";
+    zen-browser.url = "github:0xc000022070/zen-browser-flake";
+  };
+  outputs = inputs @ {
+    nixpkgs,
+    home-manager,
+    zen-browser,
+    ...
+  }: {
+    nixosConfigurations = {
+      laptop = nixpkgs.lib.nixosSystem {
+        system = "x86_64-linux";
+        modules = [
+          ./laptop/configuration.nix
+          home-manager.nixosModules.home-manager
+          {
+            home-manager.useGlobalPkgs = false;
+            home-manager.useUserPackages = true;
+            home-manager.extraSpecialArgs = {inherit zen-browser;};
+            home-manager.users.albert = import ./modules/home.nix;
+          }
+        ];
+      };
+    };
+  };
+}
+```