I did exactly same as install instruction, and :scriptnames doesn't show surround plugin. surround command doesn't work at all. Used vim8 package manager.
I followed this instruction:
mkdir -p ~/.vim/pack/tpope/start
cd ~/.vim/pack/tpope/start
git clone https://tpope.io/vim/surround.git
vim -u NONE -c "helptags surround/doc" -c q