update rust template

rust/flake.nix

@@ -0,0 +1,22 @@
+{
+  description = "Template for Rust";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=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.x86_64-linux.default = pkgs.mkShell {
+          packages = [
+            pkgs.rustup pkgs.cargo pkgs.rustc-unwrapped
+            pkgs.rust-analyzer-unwrapped
+          ];
+        };
+      }
+    );
+}