Add an official example for clicking at custom CAPTCHA coordinates.

Sometimes the Cloudflare Turnstile checkbox is not at the default location, and therefore it may be necessary to supply custom coordinates for clicking on the checkbox. There should be an official example for this.

That custom clicking code may look something like this:

 element_rect = sb.cdp.get_gui_element_rect(selector, timeout=1)
 x = element_rect["x"] + 32
 y = element_rect["y"] + 44
 sb.cdp.gui_click_x_y(x, y)