[Content]: misleading section about when derived-signals are called

從 issue 中連結的 derived-signals 文件頁面開始，將其中引用的說明與提供的 SolidJS 重現進行比較。更新措辭，使其準確描述函式何時執行，然後驗證文件中的範例及其產生的行為。

📚 Subject area/topic

concepts/derived-values/derived-signals

📋 Page(s) affected (or suggested, for new content)

https://docs.solidjs.com/concepts/derived-values/derived-signals

📋 Description of content that is out-of-date or incorrect

These functions are not executed immediately, but instead are only called when the values they rely on are changed. When the underlying signal is changed, the function will be called again to produce a new value.

I'm beginning with solidjs, so maybe I got this wrong, but I think this is at least misleading.

It is not called when count() changed (click "call inc").
It is only called, if it is explicitly called (in the example click "call double") or if it is used in a reactive context (uncomment {/*<div>double: {double()}</div>*/})

🖥️ Reproduction in StackBlitz (if reporting incorrect content or code samples)

import { render } from "solid-js/web";
import { createSignal } from "solid-js";

function App() {
    const [count, setCount] = createSignal(0);

    const inc = () => setCount(count() + 1)
    const double = () => {console.log("double called"); return count() * 2}

    return (
        <div>
            <div>count: {count()}</div>
            {/*<div>double: {double()}</div>*/}
            <button onClick={() => inc()}>call inc</button>
            <button onClick={() => double()}>call double</button>
        </div>
    );
}

render(() => <App />, document.getElementById('app'));