qmake's documentation doesn't mention QML_IMPORT_PATH

I know QML_IMPORT_PATH is for QtCreator to use, but since it's something that the developer would add to the .pro file, that means qmake must support it. Typically, all variables supported by qmake, even if it's just for QtCreator, should be documented in qmake's documentation.

Currently, this is the only documentation I can find on QML_IMPORT_PATH: https://doc.qt.io/qtcreator/creator-qml-modules-with-plugins.html

There should be some mention of it in qmake's documentation and a link back to this Creator page.