How to import installed QML plugin

[tubbadu]

Hello there! I'm trying to learn to write QML plugins following this guide.
So I cloned this project and run:

qmake-qt5
make

and running qmlscene -I imports plugins.qml correctly shows the clock
now I'd like to install this module to the whole system in order to access it from any QML project, so I run

sudo make install

it installed it correctly, so now I need to import it in my qml project:
how can I tell qmake (or cmake, even better) that I want to use it?