add nix shell

.envrc

@@ -0,0 +1 @@
+eval "$(lorri direnv)"

shell.nix

@@ -0,0 +1,14 @@
+let
+  moz_overlay = import (builtins.fetchTarball https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz);
+  nixpkgs = import <nixpkgs> { overlays = [ moz_overlay ]; };
+  channel = (nixpkgs.rustChannelOf { rustToolchain = ./rust-toolchain; });
+in
+  with nixpkgs;
+  stdenv.mkDerivation {
+    name = "genpass_shell";
+    buildInputs = [
+      channel.rust
+      cacert openssl openssh zlib
+      llvm pkgconfig git
+    ];
+  }