RPi installation requires `dosfstools` for mkfs.vfat

I was setting a RPi system with ESPRESSObin & Arch Linux ARM. The first try resulted in unbootable uSD. So I paid some attention on my second try, and I saw an error during Getting /dev/mmcblk0 ready for rpi3...:

mount: /var/tmp/manjaro-arm-installer/boot: wrong fs type, bad option, bad superblock on /dev/mmcblk0p1, missing codepage or helper program, or other error.

When I tried to format boot partition myself of course I got this error:

bash: mkfs.vfat: command not found

pacman -S dosfstools fixed this issue.

Probably worth to add this package to README.md#Dependencies.