This can be done by simply editing crontab of user explain: Of course you could add init script to handle starting it, but I found that cronjob @reboot works just as well, at least for my usecases.
That was longer than I expected, but I think it is descriptive enough so that you could use it even if you're not on ubuntu, or not using nginx, or just use anything differently.
At the moment we need to install one more thing – Pg:: Explain library.
We'll do it using Perls package manager (well, kinda) – cpan.
If you get “Sorry, but no results was found in database for this page." – it means you're good, there just aren't any plans in yet.