Custom report code goes where?

Was reading thru this:
https://slimstat.freshdesk.com/support/solutions/articles/5000528531-how-do-i-add-my-own-custom-reports-to-slimstat-

Does custom report code at above link above get added as a regular plugin in /wp-content/plugins/ or does it get added to slim stat folder somewhere?

Thanks

https://wordpress.org/plugins/wp-slimstat/