Interesting, the package does not contain any service file. Please do the following (can be done from sub shell from the error prompt as well):
cat << '_EOF_' > /etc/systemd/system/hostapd.service
[Unit]
Description=Advanced IEEE 802.11 AP and IEEE 802.1X/WPA/WPA2/EAP Authenticator
After=network.target
[Service]
Type=forking
PIDFile=/run/hostapd.pid
Restart=on-failure
RestartSec=2
Environment=DAEMON_CONF=/etc/hostapd/hostapd.conf
EnvironmentFile=-/etc/default/hostapd
ExecStart=/usr/sbin/hostapd -B -P /run/hostapd.pid -B $DAEMON_OPTS ${DAEMON_CONF}
[Install]
WantedBy=multi-user.target
_EOF_
systemctl daemon-reload