docs: add addendum on useId usage with computed

[bencodezen]

Description of Problem

There is currently no documentation around how useId() can cause errors in computed() due to conflicting instances.

Proposed Solution

Since this is something people will likely run into, a warning callout is proposed to help users avoid this problem going forward.

Additional Information

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[brc-dd]

LGTM. Though the ModelRef formatting can be reverted if prettier didn't update it 👀

[brc-dd]

Though more that I think, using useId with computed won't make much sense for anyone. Like if you have a static suffix/prefix, then why not just concat it const ariaDescribedBy = `${id}-description`. And if you don't have a static string, then why not use computed to generate a unique key from other refs/props. And if you don't have a unique static string, then why not just use useId alone. Maybe we should just remove the example 😅. The warning itself is fine.

[bencodezen]

Thanks for the review @brc-dd!