Archlinux forums do not support official installation for Raspberry Pi 3. To make the partitions on the SD card follow this link. A useful command is lsblk to see the partitions on your system. On any linux distro make sure to be careful otherwise you may flash your hard drive.
All steps can be easily applied using sudo, make sure for the step 5 to login as root using sudo su.
After making the partitions on the SD card, remove the card from your PC and insert it to the Raspberry Pi. Go to this installation guide and follow the steps.
If you are not planning to make a headless installation login as root with password root.
passwd. Then remove /etc/localtime file and symlink your local time using ln -s /usr/share/zoneinfo/Europe/Athens /etc/localtime.
vi /etc/hostname and change alarmpi to your Pi's name.
vi /etc/hosts and change the line 127.0.0.1 localhost.localdomain localhost yourhostname.
tty2 using Alt+F2 and run ls -R / && ls -R / && ls -R /
tty1 and run pacman-key --init
pacman -Syu
sudo using pacman -S sudo
EDITOR=vi visudo and uncomment the line %wheel ALL=(ALL) ALL
useradd -m -G wheel -s /bin/bash newuser
passwd newuser
logout as root and login as regular user
fakeroot package to checkupdates for Archlinux updates
xorg using sudo pacman -S xorg xorg-xinit xorg-server xorg-server-utils xterm
xfce desktop sudo pacman -S xfce4
vim and emacs
sudo pacman -S vim emacs
sudo pacman -S python python2 gcc
~/.xinitrc the line exec startxfce4 to enter to xfce using startx.
networkmanager and network-manager-applet for wifi
systemd
systemctl enable NetworkManager.service
systemctl start NetworkManager.service
nmcli dev wifi connect <name> password <password>