File: install/linux/docker-ce/ubuntu.md

The manual instructs to add the gpg 0EBFCD88 but the arm64 docker packages for ubuntu xenial are in fact signed with the key 7EA0A9C3F273FCD8. I had to run

gpg --recv-keys 7EA0A9C3F273FCD8 --keyserver sks.keyserver.org
gpg --export --armor 7EA0A9C3F273FCD8 | apt-key add - 

in order to get apt update to complete successfully