Go to https://github.com/docker/compose/releases to determine the lastest stable version of docker compose. Let's say the latest stable version is 1.25.4. Issue the following command to install docker-compose.
curl -L "https://github.com/docker/compose/releases/download/1.25.4/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose
Give docker-compose execute permission.
chmod +x /usr/local/bin/docker-compose
You should now be able to use the docker-compose command.