Docs: Mention "eslint.experimental.useFlatConfig" for IDE Settings

[lewxdev]

In the Editor Integrations - Visual Studio Code section of the docs it fails to mention the following configuration

// .vscode/settings.json
{
  // ...
  "eslint.experimental.useFlatConfig": true
}

It appears to be necessary for the latest version (I am running v2.4.4) of the extension to get lint problems to show in the editor. This may not be necessary in the future, as there is an existing pre-release for v3+ that moves this out of "experimental" see the release notes on the extension

Reasoning: The docs currently recommend using the flat config and should at least mention how to get it fully working in Visual Studio Code. (plus, it took me too long to figure out I needed this in my project 😅)

[ota-meshi]

I don't think there is any need to explain the experimental settings. The flat config is not recommended as it is not yet GA. It is better to wait for the release of ESLint v9.

[lewxdev]

ESLint v9 is out

[ota-meshi]

I don't think eslint.experimental.useFlatConfig is needed in ESLint v9.