build(nix/flake): adding the flake to build all the nix stuff

.envrc

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+use flake

flake.nix

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+{
+	description = "Shell for inception 42 project";
+
+	inputs = {
+		nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+		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 = "inception-42";
+					buildInputs = with pkgs; [
+						docker
+						docker-compose
+						htop
+						vim
+						zsh
+						openssl
+						curl
+					] ++ (
+						if pkgs.stdenv.isLinux then [
+							valgrind
+						] else []
+					);
+					
+					shellHook = ''
+						export CXX=clang++
+						export CXXFLAGS="-std=cpp98 -Wall -Werror -Wextra"
+						printf "\n\033[0;90mCPP env loaded for: \033[38;5;220m${system}\033[0m\n"
+					'';
+					};
+				}
+		);
+}