Make it clearer how to run an effect only once (componentDidMount style)

Based on this conversation on Twitter, it's perhaps not clear enough how to make an effect hook only run once on mount (a la componentDidMount.)

The relevant info on how to do it properly is tucked away near the bottom of the effect hook doc, in a footnote of this tip. This is a major use case that should probably have higher priority in the documentation. I imagine a vast majority of apps actually need to do use an effect in this manner.

I assume people are probably doing something like

function MyComponent({ fetchData, data }) {
  useEffect(() => {
    if (!data) {
      fetchData()
    }
  })
}

I can make the change to the docs, but where's the best place to put it? Should I make it a tip? Does it deserve higher priority than that?

从 effect hook 文档及其中的“提示：通过跳过 Effect 优化性能”部分开始，目前只在 mount 时运行一次的指导被隐藏在这里。判断 useEffect-on-mount 示例是否应放在优先级更高的部分或提示中，然后确认文档清楚地解释了预期的模式。