Update systemd unit file to install /var/run/fw-daemon/ on start

sources/lib/systemd/system/fw-daemon.service

@@ -1,10 +1,11 @@
 [Unit]
+Documentation=https://github.com/subgraph/fw-daemon
 Description=Subgraph Firewall Daemon
 
 [Service]
 Environment="GODEBUG=cgocheck=0"
+ExecStartPre=/usr/bin/install -d /var/run/fw-daemon
 ExecStart=/usr/sbin/fw-daemon
-ExecReload=/bin/kill -HUP ${MAINPID}
 
 [Install]
 WantedBy=multi-user.target