Mount Arch Linux ISO, copy files:

cp /mnt/arch/boot/x86_64/archiso.img /tftpboot/arch/
cp /mnt/arch/boot/x86_64/vmlinuz /tftpboot/arch/
cp -r /mnt/* /var/www/html/arch/

PXE config example /tftpboot/pxelinux.cfg/default:

serial 0 115200
default arch64
prompt 0
timeout 0

LABEL arch64
        KERNEL arch/vmlinuz
        INITRD arch/archiso.img
        APPEND ip=dhcp archiso_http_srv=http://<your server IP> archisobasedir=/arch/arch console=ttyS0,115200n8
        IPAPPEND 3