Update appendix.rst

[waldo323]

"make sure docker containers are stopped" using "sudo systemctl restart docker" will restart the containers and won't leave them in a stopped state. changing this to "sudo systemctl stop docker" will have better results.

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[waldo323]

I see another change which would allow the command to run properly. - with only sudo there can be an error when trying to stop the docker service so using sudo su -c "systemctl stop docker" will be an improvement