install gitlabn on centos code example

Example: install gitlab runner on centos

curl -L "https://packages.gitlab.com/install/repositories/runner/gitlab-runner/script.rpm.sh" | sudo bash
export GITLAB_RUNNER_DISABLE_SKEL=true; sudo -E yum install gitlab-runner
yum list gitlab-runner --showduplicates | sort -r
export GITLAB_RUNNER_DISABLE_SKEL=true; sudo -E yum install gitlab-runner-10.0.0-1