Add browser tab open focus example

This example shows how to make i3wm automatically switch to a browser that
has opened a new tab by using the new ipc "title change" event. This event
will be available in the next released version (after 4.7.2).

If you have a webpage open that changes the title without any user
interaction (rare, but possible), you may need to do some additional
filtering so it does not switch focus unexpectedly.