Move all files to reading-college/demo/

reading-college/demo/flake.nix

@@ -0,0 +1,31 @@
+{
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs =
+    { nixpkgs, ... }:
+    let
+      system = "x86_64-linux";
+      pkgs = nixpkgs.legacyPackages.${system};
+    in
+    {
+      devShells.${system}.default =
+        let
+          php = pkgs.php83.buildEnv {
+            extraConfig = ''
+              memory_limit = 512M
+            '';
+          };
+          phpPackages = pkgs.php83Packages;
+        in
+        pkgs.mkShell {
+          packages = with pkgs; [
+            php
+            phpPackages.composer
+            simple-http-server
+            sqlite
+          ];
+        };
+
+      formatter.${system} = pkgs.nixfmt-classic;
+    };
+}