dnsmasq: Add reverse lookup to example

[Monviech]

https://forum.opnsense.org/index.php?topic=47126.msg237125#msg237125

[Pataps]

Hi, I came across "additional context" in opnsense/core#8455 while I was configuring Dnsmasq. I think it would be beneficial to have an easier way to understand different options meaning, as current help text for "ra mode" field is quite vague. How about publishing something similar in the official docs? If it makes more sense to have this in separate ticket, I'm happy to create one.

[Monviech]

Sure create a separate ticket and Ill look into it. I kept it vague since the explanation in dnsmasq manpage is very long.