add yum-utils for Red Hat & CentOS

[strouja]

I also suggest removing the $ in front of each command so end users can simply copy and paste the line without having to edit and remove the $ If you do not like my suggestions I won't be offended.

yum-config-manager will fail unless yum-utils is installed as yum-config-manager is installed with yum-utils. If yum-utils is already installed then the yum install -y yum-utils is harmless

Great job with the tool and I love it. Thanks for everything