Tweak CTK_SUPERBUILD option description text.
Tweak CTK_SUPERBUILD option description text.

See #418

naucoin/CTK,rkhlebnikov/CTK,ddao/CTK,SINTEFMedtek/CTK,AndreasFetzer/CTK,sankhesh/CTK,151706061/CTK,naucoin/CTK,SINTEFMedtek/CTK,SINTEFMedtek/CTK,laurennlam/CTK,msmolens/CTK,pieper/CTK,msmolens/CTK,pieper/CTK,mehrtash/CTK,espakm/CTK,CJGoch/CTK,Heather/CTK,danielknorr/CTK,ddao/CTK,ddao/CTK,AndreasFetzer/CTK,SINTEFMedtek/CTK,jcfr/CTK,espakm/CTK,commontk/CTK,Sardge/CTK,laurennlam/CTK,AndreasFetzer/CTK,rkhlebnikov/CTK,151706061/CTK,mehrtash/CTK,pieper/CTK,jcfr/CTK,151706061/CTK,SINTEFMedtek/CTK,msmolens/CTK,danielknorr/CTK,rkhlebnikov/CTK,Heather/CTK,mehrtash/CTK,commontk/CTK,naucoin/CTK,fedorov/CTK,Heather/CTK,151706061/CTK,fedorov/CTK,Sardge/CTK,CJGoch/CTK,espakm/CTK,ddao/CTK,sankhesh/CTK,CJGoch/CTK,151706061/CTK,commontk/CTK,CJGoch/CTK,sankhesh/CTK,Sardge/CTK,msmolens/CTK,sankhesh/CTK,rkhlebnikov/CTK,jcfr/CTK,jcfr/CTK,AndreasFetzer/CTK,pieper/CTK,CJGoch/CTK,commontk/CTK,danielknorr/CTK,Sardge/CTK,jcfr/CTK,mehrtash/CTK,laurennlam/CTK,Heather/CTK,danielknorr/CTK,fedorov/CTK,naucoin/CTK,fedorov/CTK,laurennlam/CTK,espakm/CTK