[stdlib] Update SubSequence docs
[stdlib] Update SubSequence docs

parkera/swift,apple/swift,roambotics/swift,apple/swift,roambotics/swift,rudkx/swift,parkera/swift,benlangmuir/swift,xwu/swift,xwu/swift,glessard/swift,hooman/swift,roambotics/swift,hooman/swift,roambotics/swift,atrick/swift,rudkx/swift,gregomni/swift,parkera/swift,ahoppen/swift,gregomni/swift,glessard/swift,hooman/swift,ahoppen/swift,hooman/swift,JGiola/swift,JGiola/swift,atrick/swift,xwu/swift,ahoppen/swift,roambotics/swift,rudkx/swift,rudkx/swift,JGiola/swift,JGiola/swift,benlangmuir/swift,benlangmuir/swift,gregomni/swift,xwu/swift,ahoppen/swift,glessard/swift,glessard/swift,atrick/swift,parkera/swift,atrick/swift,glessard/swift,rudkx/swift,atrick/swift,hooman/swift,xwu/swift,xwu/swift,gregomni/swift,benlangmuir/swift,parkera/swift,apple/swift,parkera/swift,apple/swift,apple/swift,benlangmuir/swift,JGiola/swift,rudkx/swift,parkera/swift,JGiola/swift,atrick/swift,glessard/swift,xwu/swift,roambotics/swift,hooman/swift,apple/swift,hooman/swift,gregomni/swift,gregomni/swift,benlangmuir/swift,ahoppen/swift,parkera/swift,ahoppen/swift