Build tool suggestion: also generate service file?

@abiosoft per your suggestion, I tried your build tool. I already have a service file standard in place where I use Caddy; you might want to attempt generating one that folks could modify for their needs?

Related suggestion: maybe also a suggestion to the user to **/sbin/setcap CAP_NET_BIND_SERVICE=+eip (installed caddy binary)** ?

```
[Unit]
Description=Caddy
After=network.target
[Service]
Type=simple
LimitNOFILE=8192
ExecStartPre=/bin/mkdir -p /tmp/caddy_cache
ExecStart=/usr/local/bin/caddy -conf /etc/default/caddy
ExecReload=/usr/bin/pkill -USR1 caddy
User=caddy
Group=caddy
[Install]
WantedBy=multi-user.target
```