Tweak examples

[proger]

Add a mention how to configure Github OAuth App to README and add $/monad to lib.urp to make sure it builds.

I was using the following nix expression to build:

{ stdenv, fetchgit, autoreconfHook, curl, urweb }:

stdenv.mkDerivation {
  name = "urweb-world";

  buildInputs = [
    autoreconfHook
    urweb
  ];

  propagatedBuildInputs = [
    curl
  ];

  preConfigure = ''
    export CFLAGS="-I${urweb}/include/urweb"
  '';

  src = ./world;
  # src = fetchgit {
  #   inherit (builtins.fromJSON (builtins.readFile ./world.json)) url rev sha256;
  # };
}