Minor cmake tweaks and comment improvements
Minor cmake tweaks and comment improvements

cwilling/oiio,scott-wilson/oiio,mcanthony/oiio,OpenImageIO/oiio,scott-wilson/oiio,YangYangTL/oiio,mcanthony/oiio,scott-wilson/oiio,sambler/oiio,lgritz/oiio,bdeluca/oiio,cwilling/oiio,lgritz/oiio,micler/oiio,YangYangTL/oiio,OpenImageIO/oiio,micler/oiio,bdeluca/oiio,micler/oiio,lgritz/oiio,micler/oiio,mcanthony/oiio,sambler/oiio,bdeluca/oiio,lgritz/oiio,cwilling/oiio,bdeluca/oiio,sambler/oiio,mcanthony/oiio,YangYangTL/oiio,scott-wilson/oiio,OpenImageIO/oiio,OpenImageIO/oiio,YangYangTL/oiio,cwilling/oiio,sambler/oiio