You can add any file or folder you like to the catalogue. hmelman's
user guide explains how.
By the way, it is not usually recommended that you add an entire drive
to the QS catalogue. It is usually better to add specific folders
that you use regularly. Generally speaking, adding a whole drive will
1) add many unnecessary items to the catalogue and thereby clutter up
your search results list, and 2) needlessly reduce performance by
requiring QS to sort through all those extra files.