add templates as flake output

templates/rust/flake.nix

@@ -0,0 +1,38 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    flake-utils = {
+      url = "github:numtide/flake-utils";
+    };
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs = {
+        nixpkgs.follows = "nixpkgs";
+      };
+    };
+  };
+  outputs = {
+    flake-utils,
+    nixpkgs,
+    rust-overlay,
+    ...
+  }:
+    flake-utils.lib.eachDefaultSystem (system: let
+      pkgs = import nixpkgs {
+        inherit system;
+        overlays = [(import rust-overlay)];
+      };
+      rustToolchain = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
+      rustPlatform = pkgs.makeRustPlatform {
+        cargo = rustToolchain;
+        rustc = rustToolchain;
+      };
+    in {
+      devShells.default = pkgs.mkShell {
+        packages = with pkgs; [
+          rust-analyzer
+          rustToolchain
+        ];
+      };
+    });
+}