feat: add welcome message

Direct people to upgrade their systems first and link to support channels just in case.

flake.nix

@@ -26,23 +26,27 @@
       };
       nixosModules.default = self.nixosModules.wsl;
 
-      nixosConfigurations = {
+      nixosConfigurations = let
+        initialConfig = {
+          wsl.enable = true;
+
+          programs.bash.loginShellInit = "nixos-wsl-welcome";
+        };
+      in {
         modern = nixpkgs.lib.nixosSystem {
           system = "x86_64-linux";
           modules = [
             self.nixosModules.default
-            { wsl.enable = true; }
+            initialConfig
           ];
         };
 
         legacy = nixpkgs.lib.nixosSystem {
           system = "x86_64-linux";
           modules = [
             self.nixosModules.default
-            {
-              wsl.enable = true;
-              wsl.nativeSystemd = false;
-            }
+            initialConfig
+            { wsl.nativeSystemd = false; }
           ];
         };
 

modules/default.nix

@@ -6,6 +6,7 @@
     ./recovery.nix
     ./systemd
     ./version.nix
+    ./welcome.nix
     ./wsl-conf.nix
     ./wsl-distro.nix
 

modules/welcome.nix

@@ -0,0 +1,21 @@
+{ lib, pkgs, config, ... }:
+let
+  welcomeMessage = pkgs.writeText "nixos-wsl-welcome-message" ''
+    Welcome to your new NixOS-WSL system!
+
+    Please run `sudo nix-channel --update` and `sudo nixos-rebuild switch` now, to ensure you're running the latest NixOS and NixOS-WSL versions.
+
+    If you run into issues, please report them on our Github page at https://github.com/nix-community/NixOS-WSL or come talk to us on Matrix at #wsl:nixos.org.
+
+    ❄️ Enjoy NixOS-WSL! ❄️
+
+    Note: this message will disappear after you rebuild your system. If you want to see it again, run `nixos-wsl-welcome`.
+  '';
+  welcome = pkgs.writeShellScriptBin "nixos-wsl-welcome" ''
+    cat ${welcomeMessage}
+  '';
+in {
+  config = lib.mkIf config.wsl.enable {
+    environment.systemPackages = [ welcome ];
+  };
+}