Add Nix-OS specific files

.envrc

@@ -0,0 +1 @@
+use nix

shell.nix

@@ -0,0 +1,14 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+let
+  dotnet = pkgs.dotnetCorePackages.sdk_8_0;
+in
+pkgs.mkShell {
+  buildInputs = [ dotnet ];
+
+  shellHook = ''
+    export DOTNET_ROOT="${dotnet}/share/dotnet"
+    export PATH="${dotnet}/bin:$PATH"
+  '';
+}
+