install docker cli on centos code example

Example: docker on centos7

# To install docker on centos 7 or SL7
# From https://docs.docker.com/engine/install/centos/
sudo yum install -y yum-utils
sudo yum-config-manager \
    --add-repo \
    https://download.docker.com/linux/centos/docker-ce.repo
# From https://stackoverflow.com/questions/45272827/docker-ce-on-rhel-requires-container-selinux-2-9
# You must add the latest container-selinux form http://mirror.centos.org/centos/7/extras/x86_64/Packages/
# This version is correct as of 11-3-2020:
sudo yum install -y \
    http://mirror.centos.org/centos/7/extras/x86_64/Packages/container-selinux-2.119.2-1.911c772.el7_8.noarch.rpm
# Now you can continue w/ the Docker installation
sudo yum install -y docker-ce docker-ce-cli containerd.io
# To start and check the version
sudo systemctl start docker
sudo systemctl enable docker
sudo docker -v