Unclear docs on how to use this with FlatESLintConfig

[AndreaPontrandolfo]

PROBLEM

I'm trying to use this in my FlatConfig, but without success. Looking at the latest PRs, this should be supported, but in the docs there is no such mention, even less so an explanation for complex usage.
For reference, this is where i'm trying to use it: https://github.com/AndreaPontrandolfo/sheriff/blob/master/configs/eslint.config.js

PROPOSED SOLUTION

Expand the docs on how to use this with the FlatConfig, also for complex usage.

[Shinigami92]

@sxzz is responsible for the flat-config support

[sxzz]

It's pretty easy. Use defineFlatConfig then works