ArchLinux prerequisites not available outside AUR

GraphicsMagick, the exif tool, minio and runit aren't available in the Arch core repositories.

GraphicsMagick (graphicsmagick), Exiftool (perl-image-exiftool), MinIO (minio) and runit (runit-systemd) are available in the AUR. Packages from the AUR can't be installed with pacman so the instructions are wrong.

An AUR package manager (like pacaur) is recommended for installing packages from the AUR.