Explain the exit-on-X-server-shutdown trick

client.c

@@ -102,6 +102,8 @@ osd_wait(int delay)
       poll(&pfd, 1, wait_until - now);
       if (pfd.revents & POLLIN)
 	{
+	  // We use the event loop only to detect that the X server has been shut down.
+	  // In such cases, xlib raises an error and exits.
 	  XEvent ev;
 	  while (XPending(dpy))
 	    XNextEvent(dpy, &ev);