Update readme with new plugin syntax
Update readme with new plugin syntax

shaunstanislaus/tpm,GeoffMaciolek/tpm,cclay/tpm,zer4tul/dotfiles,larrylv/tpm,zer4tul/dotfiles,joshuarubin/dotfiles,bruno-/tpm,joshuarubin/dotfiles,dxq-git/tpm,joshuarubin/dotfiles,tmux-plugins/tpm,joshuarubin/dotfiles