clarify generated comment

manager/dist/Library/LaunchDaemons/_rdns_.plist.tmpl

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!-- Generated for serviceman. Edit as you wish. -->
+<!-- Generated for serviceman. Edit as you wish, but leave this line. -->
 <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <plist version="1.0">
 <dict>

manager/dist/etc/systemd/system/_name_.service.tmpl

@@ -1,4 +1,4 @@
-# Generated for serviceman. Edit as you wish.
+# Generated for serviceman. Edit as you wish, but leave this line.
 # Pre-req
 # sudo mkdir -p {{ .Local }}/opt/{{ .Name }}/ {{ .Local }}/var/log/{{ .Name }}
 {{ if .System -}}