Update targetOS docs with the full list of possible OS values.
Update targetOS docs with the full list of possible OS values.

This now matches what's in evaluatorscriptclass.cpp and includes iOS
Simulator which was added with the targetOS/hostOS change.

Change-Id: I5269fbe5d8a859cd22235a9f10c4328e32b103cf
Reviewed-by: Joerg Bornemann <47777b9406dbddd02a3fdca8341789a013805a11@digia.com>

qt-labs/qbs,gatzka/qt-labs-qbs,Distrotech/qbs,Distrotech/qbs,villytiger/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,Distrotech/qbs,villytiger/qbs,villytiger/qbs,villytiger/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,gatzka/qt-labs-qbs,villytiger/qbs,qtproject/qt-labs-qbs,Distrotech/qbs,gatzka/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,Distrotech/qbs,Distrotech/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,qt-labs/qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,Distrotech/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,villytiger/qbs