Configure:
cd /srv;
mkdir tftp;
chmod 777 -R tftp;
chown nobody:nogroup -R tftp;
and then download image:
cd /srv/tftp/
wget http://ftp.nl.debian.org/debian/dists/jessie/main/installer-amd64/current/images/netboot/netboot.tar.gz
tar xfz netboot.tar.gz
wget http://ftp.nl.debian.org/debian/dists/jessie/main/installer-amd64/current/images/SHA256SUMS
wget http://ftp.nl.debian.org/debian/dists/jessie/Release
wget http://ftp.nl.debian.org/debian/dists/jessie/Release.gpg