Add portable build file

Author: Javier-varez

portable_build.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+set -e
+
+curl -L https://github.com/DavHau/nix-portable/releases/latest/download/nix-portable-$(uname -m) > ./nix-portable
+chmod +x ./nix-portable
+
+./nix-portable nix build
+./nix-portable nix-shell -p bash --run "cp -rL result public"