When using Qt from distribution packages

[ci skip]

README.md

@@ -249,6 +249,10 @@ Here, `CONFIG+=use_qt_paths` needs to be removed, otherwise it will install ever
 
 The exception is that you are building Qt libraries that _should_ be installed to the same location where Qt resides on your system, from where it will be picked up by `linuxdeployqt`.
 
+### When using Qt from distribution packages
+
+On Ubuntu 14.04, you will need to pass in `-qmake=/usr/lib/x86_64-linux-gnu/qt5/bin/qmake` when using distribution packages.
+
 ### A note on DESTDIR
 
 According to https://dwheeler.com/essays/automating-destdir.html,