README: add QMPlay2 to list of projects using libass
README: add QMPlay2 to list of projects using libass

Closes #225.

ShiftMediaProject/libass,xbmc/libass,MrSmile/libass,astiob/libass,grigorig/libass,grigorig/libass,Akemi/libass,xbmc/libass,ShiftMediaProject/libass,MrSmile/libass,libass/libass,Akemi/libass,Akemi/libass,libass/libass,astiob/libass