Add a PHP 8.1 devshell

flake.nix

@@ -13,6 +13,7 @@
 
       imports = [
         ./modules/nodejs.nix
+        ./modules/php81.nix
         ./modules/php82.nix
         ./modules/php83.nix
         ./modules/tailwindcss.nix

modules/php81.nix

@@ -0,0 +1,17 @@
+{
+  perSystem =
+    { pkgs, ... }:
+    {
+      devShells.php81 = pkgs.mkShell {
+        packages = with pkgs; [
+          php81
+          php81Packages.composer
+          phpactor
+        ];
+
+        shellHook = ''
+          php --version
+        '';
+      };
+    };
+}