Just wondering whether you are your own ISP or if your ISP delegated a larger public IP range to you, including reverse DNS zone? If yes, you don’t need an example in the docs, because then you probably know how to manage your reverse zone.
If the above does not apply to you, then the reverse DNS zone is manged by your ISP or your hosting provider, which means you can’t setup a PTR record yourself, but your ISP / hosting provider has to do it for you.
And of course the hostname of your server must appear in the PTR record. A PTR record basically does the same thing as the A record, but it does it the other way around. It points from the IP to a domain name or to a FQDN. Here’s an example:
188.8.131.52.in-addr.arpa. IN PTR mail.example.com.