docs(tabs): mention that index needs to be number
docs(tabs): mention that index needs to be number

Closes #5876

shootermv/bootstrap,wesleycho/bootstrap,Kpler/bootstrap,caoruiy/bootstrap,angular-ui/bootstrap,angular-ui/bootstrap,BookingBug/bootstrap,looker/bootstrap,vfiles/bootstrap,wesleycho/bootstrap,shootermv/bootstrap,fpipita/bootstrap,looker/bootstrap,BookingBug/bootstrap,Servoy/bootstrap,byronigoe/bootstrap,Kpler/bootstrap,RobJacobs/bootstrap,caoruiy/bootstrap,RobJacobs/bootstrap,byronigoe/bootstrap,icfantv/bootstrap,fpipita/bootstrap,vfiles/bootstrap,Servoy/bootstrap,icfantv/bootstrap