Setup repository in Arch Linux

This is my first time to install Arch Linux. At the first boot, I use "pacman -S gnome" command to install gnome desktop enviroment. But its show error message that is "no package found". I found that I have not setup the respository. So, refer to arch wiki. Edit this file - "/etc/pacman.d/mirrorlist", find out your locale and unmark the suitable repository server. Like this:
# Taiwan
Server = http://shadow.ind.ntou.edu.tw/archlinux/