add repo for CentOS

转载自：http://www.cnblogs.com/smartvessel/archive/2012/09/05/2671796.html

cd /etc/yum.repos.d/ 
mv CentOS-Base.repo CentOS-Base.repo.back
wget http://mirrors.163.com/.help/CentOS6-Base-163.repo
mv CentOS6-Base-163.repo CentOS-Base.repo
yum makecache