Add "docker-purge" command to my functions

[andreffs18]

Source: https://medium.com/@wlarch/no-space-left-on-device-when-using-docker-compose-why-c4a2c783c6f6

1- Stop all containers

• docker stop $(docker ps -aq)

2- Remove all containers

• docker rm $(docker ps -aq)

3- Prune system

• docker system prune -a --volumes

4- Remove all images

• docker rmi $(docker images -q)