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

从 issue 中链接的 derived-signals 文档页面开始，将其中引用的解释与提供的 SolidJS 复现进行比较。更新措辞，使其准确描述函数何时运行，然后验证文档中的示例及其产生的行为。

📚 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📋 Description of content that is out-of-date or incorrect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'));