Add Nix and environment configuration files

- Created `.envrc` for Direnv integration to manage Nix environment.
- Added `.gitignore` to exclude build artifacts and IDE files.
- Introduced `flake.nix` for Nix flake configuration and development shell setup.
- Generated `flake.lock` to lock dependencies for the Nix environment.
- Updated `go.mod` to specify Go version 1.23.
- Added `README.md` with project overview, development instructions, and troubleshooting tips.

flake.nix

@@ -0,0 +1,21 @@
+{
+  description = "ARR Go Client - A Go client for ARR applications";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
+
+  outputs = { self, nixpkgs }:
+    let
+      system = "x86_64-linux";
+      pkgs = nixpkgs.legacyPackages.${system};
+    in
+    {
+      devShells.${system}.default = pkgs.mkShell {
+        buildInputs = with pkgs; [
+          go_1_23
+        ];
+      };
+    };
+}
+