document how statement can be used in match arms with hml fragments

[Madoshakalaka]

I don't think this is very intuitive

#[function_component]
pub fn Foo() -> Html {
    html! {
        match true {
            true =>  <>
                let a = 1;
                let b = 2;

                    <div>{a + b}</div>
            </>,
            false =>  <div>{"false"}</div>,
        }
    }
}