Draft guidance section for aria-haspopup

[mcking65]

The ARIA 1.0 guidance section can be seen here: https://rawgit.com/w3c/aria-practices/master/aria-practices-DeletedSectionsArchive.html#relations_haspopup

aria-haspopup changes considerably with 1.1 as do practices related to elements that trigger popups. So, the 1.0 guidance may not be very useful as a starting point.

It is possible the APG does not need a separate section on haspopup as its use may be adequately described and demonstrated in the example design patterns.