Add link to exfat-fuse for ARM-based Synology devices

[trzimm]

Some Synology devices have ARM CPUs

$ uname -m
armv7l

Debian.org provides arm-based versions of the fuse-exfat package: http://http.us.debian.org/debian/pool/main/f/fuse-exfat/

Helpful for some users who don't have amd64-based Synology devices.