Add SwiftUI Category under Using Swift Category

[Lantua]

For more context on the current policy,

@John_McCall

Questions that are primarily about using Apple APIs should be asked on the Apple developer forums. That’s been our policy here, at Apple’s request, since the moment these forums were created.

I guess it would be debatable if SwiftUI becomes open-source; if.

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Personally, I used to tell people to go to appropriate forums all the time in the past, but the sheer quantity of people coming in (or ignoring the suggestions) is just exhausting.