[neon] qt 5.6.0 usedition testing

[Harald Sitter]

ahoy

We are currently looking at integrating Qt 5.6.0 as Qt 5.6.1's release
was pushed into later this month. Before we land it by default we'd
like to do some testing. If you are using the user edition tech
preview you can add a testing repository and do an update to get Qt
5.6.0 and a bunch of Plasma updates. Beware that this might entirely
break your system, so only do this if you are comfortable with
potentially repairing the system by hand or have nothing much to lose.

sudo add-apt-repository http://archive.neon.kde.org/tmp/testing
sudo apt update
sudo apt dist-upgrade

If you are using one of the developer editions you will probably get
Qt 5.6.0 as an update some time this week, once we are confident it
won't break everything and the kitchen sink.

HS