Added a nix dev env for faster integration test turnaround

.envrc

@@ -0,0 +1,2 @@
+use flake 'github:DavidM-D/workspaces?dir=rust'
+use flake .

README.md

@@ -40,6 +40,12 @@ git submodule update --init --recursive
 docker build . -t near/mpc-recovery
 ```
 
+alternatively if you have [nix](https://nixos.org/) and [direnv](https://direnv.net/) installed, you can set up a development environment by running:
+
+``` BASH
+direnv allow
+```
+
 Run tests with:
 ```
 cargo test -p mpc-recovery

flake.nix

@@ -0,0 +1,29 @@
+# This is a simple deterministic rust development environment
+# This exposes Cargo, rustfmt, rust-analyzer and clippy
+# This does not allow you to build binaries using nix
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+    rust-overlay.url = "github:oxalica/rust-overlay";
+  };
+  outputs = { self, nixpkgs, flake-utils, rust-overlay, ... }:
+
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        overlays = [ (import rust-overlay) ];
+        pkgs = import nixpkgs { inherit system overlays; };
+
+        # Pick what rust compiler to use
+      in {
+        devShell = pkgs.mkShell {
+
+          # Everything in this list is added to your path
+          buildInputs =
+            with pkgs; [
+              darwin.apple_sdk.frameworks.Security
+              protobuf
+            ];
+        };
+      });
+}