docs: update return type

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brisa-adapter-vercel

``` bun add https://pkg.pr.new/brisa-build/brisa/brisa-adapter-vercel@621 ```

create-brisa

``` bun add https://pkg.pr.new/brisa-build/brisa/create-brisa@621 ```

brisa-tailwindcss

``` bun add https://pkg.pr.new/brisa-build/brisa/brisa-tailwindcss@621 ```

brisa-pandacss

``` bun add https://pkg.pr.new/brisa-build/brisa/brisa-pandacss@621 ```

www

``` bun add https://pkg.pr.new/brisa-build/brisa/www@621 ```

brisa

``` bun add https://pkg.pr.new/brisa-build/brisa@621 ```

commit: 0b8c18a