[doc] explain how to add interleaving sliding window support

[youkaichao]

to avoid the case of #11583 happening again.

[github-actions]

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[DarkLight1337]

Any chance you can review and merge #11755 first since that PR will move this page?

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @youkaichao.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[youkaichao]

@DarkLight1337 done

[DarkLight1337]

Thanks for adding this!

[DarkLight1337]

Docs look good, let's force-merge this.