The repository moved from debian.griffo.io to deb.griffo.io (Debian
trademark policy). Also switch to the current signing key, the
keyring + signed-by layout, add the missing sudo and apt update, and
apply the same fix to the French README.
* docs: add logo
* docs: add a full header
* docs: replace dash with em dash
* docs: use current color fill instead of white
* docs: add seperate dark and light logos
