add default.nix/.envrc for automagic platformio dev environment on NixOS

.envrc

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

.gitignore

@@ -1,3 +1,4 @@
+.direnv
 .pio
 .vscode/.browse.c_cpp.db*
 .vscode/c_cpp_properties.json

default.nix

@@ -0,0 +1,10 @@
+{ pkgs ? import <nixpkgs> {} }:
+let
+in
+  pkgs.mkShell {
+    buildInputs = [
+      pkgs.platformio
+      # optional: needed as a programmer i.e. for esp32
+      pkgs.avrdude
+    ];
+}