docs: --min-age format isn't documented

[rrauenza]

Description I can't find in the docs where --min-age is documented, nor any examples.

I think it is based on Rust's parse_duration, though:

https://docs.rs/parse_duration/latest/parse_duration/

So I'm wondering if you might want to add a simple example, --min-age 1day and then also a link to the Rust API?

If you can confirm, I'm also willing to do a PR.

[stepchowfun]

A PR would be welcome—thank you!

[stepchowfun]

Resolved by https://github.com/stepchowfun/docuum/pull/324