added shell.nix to test

shell.nix

@@ -0,0 +1,19 @@
+# <shell.nix>
+{ pkgs ? import <nixpkgs> {}}:
+ 
+ let
+   rust_overlay = import (builtins.fetchTarball "https://github.com/oxalica/rust-overlay/archive/master.tar.gz");
+   pkgs = import <nixpkgs> { overlays = [ rust_overlay ]; };
+   ruststable = (pkgs.rust-bin.stable.latest.default.override {
+        extensions = [
+          "rust-src"
+        ];
+    });
+ in
+ pkgs.mkShell {
+   buildInputs = with pkgs; [
+     ruststable
+     rust-analyzer
+     bacon
+   ];
+ }