build(nix): adding the flake for nix

flake.nix

@@ -0,0 +1,28 @@
+{
+	description = "Shell for 42 cpp";
+
+	inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+	inputs.flake-utils.url = "github:numtide/flake-utils";
+
+	outputs = { self, nixpkgs, flake-utils }:
+		flake-utils.lib.eachDefaultSystem (system:
+			let
+				pkgs = import nixpkgs {
+					inherit system;
+				};
+			in {
+				devShells.default = pkgs.mkShell {
+					name = "cpp-42";
+					buildInputs = with pkgs; [
+						clang
+						clang-tools
+					];
+					
+					shellHook = ''
+						export CXX=clang++
+						export CC=clang
+					'';
+					};
+				}
+		);
+}