surely, more logic will help

install.sh

@@ -1,5 +1,10 @@
 #!/bin/bash
 
+if [ ! -f login-mailer.service ]; then
+  echo "have you copied and edited login-mailer.service.template?"
+  exit 1
+fi
+
 cp ./login-mailer.sh /usr/local/bin/login-mailer
 cp ./login-mailer.service /etc/systemd/system/login-mailer.service
 cp ./login-mailer.timer /etc/systemd/system/login-mailer.timer