Add flake example in README

README.md

@@ -17,6 +17,69 @@ And get a nice interactive experience.
 
 This works on any Forgejo instance.
 
+You can also set up a systemd service and timer to run every once in a while.
+
+Use the flake, like so:
+
+```nix
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+    github2forgejo = {
+      url = "github:RGBCube/GitHub2Forgejo";
+
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs = { nixpkgs, github2forgejo, ... }: let inherit (nixpkgs) lib; in {
+    nixosConfigurations.myserver = lib.nixosSystem {
+      modules = [
+        github2forgejo.nixosModules.default
+
+        {
+          nixpkgs.overlays = [ github2forgejo.overlays.default ];
+
+          services.github2forgejo = {
+            enable = true;
+
+            # Something along the lines of:
+            #
+            # GITHUB_USER="RGBCube"
+            # GITHUB_TOKEN="ghp_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+            # FORGEJO_URL="https://git.rgbcu.be/"
+            # FORGEJO_USER="RGBCube"
+            # FORGEJO_TOKEN="xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+            # STRATEGY="mirrored"
+            # FORCE_SYNC="true"
+            #
+            # Do `GITHUB_TOKEN=""` if you want to only mirror public repositories of a person.
+            # You HAVE TO set each one of these. Leaving one unset will make the systemd unit fail!
+            environmentFile = "/secrets/github2forgejo.env";
+
+            # The default runs every day at midnight. But you can override it like so:
+            #
+            # timerConfig = {
+            #   OnCalendar         = "00:05";
+            #   RandomizedDelaySec = "5h";
+            #   Persistent         = true;
+            # };
+            #
+            # Or you can disable the timer by setting `timerConfig` to null:
+            #
+            # timerConfig = null;
+          }
+        }
+      ];
+    }
+  };
+}
+```
+
+The script is also available as a package, you just need to use the
+`packages.<system>.default` or `packages.<system>.github2forgejo` outputs.
+
 ## FAQ
 
 ### What is the difference between mirroring and cloning?