Draw the help dialog.

def draw_help(self, surf):
    """Draw the help dialog."""
    if not self._help:
      return

    def write(loc, text):
      surf.write_screen(self._font_large, colors.black, loc, text)

    surf.surf.fill(colors.white * 0.8)
    write((1, 1), "Shortcuts:")

    max_len = max(len(s) for s, _ in self.shortcuts)
    for i, (hotkey, description) in enumerate(self.shortcuts, start=2):
      write((2, i), hotkey)
      write((3 + max_len * 0.7, i), description)