Add systemd service file to linux packages

build/after-install.sh

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+systemctl enable vikunja.service
+
 # Fix the config to contain proper values
 NEW_SECRET=$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1)
 sed -i "s/<jwt-secret>/$NEW_SECRET/g" /etc/vikunja/config.yml