Reconciliation docs need amendment

I think it can be clarified that the component that's rendering a React element of a new type will itself not be remounted; however, its child elements will be.

In other words if a component's render method returns

<div>
  <Counter />
</div>

when it is mounted and later (when it is updated)

<span>
  <Counter />
</span>

that component itself will not be remounted, but the <Counter/> element will be.

首先定位 issue 中討論的 reconciliation 文件部分，並查看其中關於變更渲染元素類型的說明。明確渲染元件不會被重新掛載，而其子元素會被重新掛載，並使用 div/span 範例作為驗收檢查。