[Docs]: 如何设置原点（0,0）在页面的中心位置，这个文档中没有介绍

### 📍 Which page are you reading?

https://g6.antv.antgroup.com/api/viewport#graphzoomtozoom-animation-origin

### 💭 What's on your mind?

Could be clearer / 需要更清晰的解释

### 🤔 Tell us more

找了好几个小时，没找到将坐标原点（0， 0）设置在页面的正中心的办法

### 💡 Got any suggestions?

_No response_

Open the linked Viewport documentation at the Graph.zoomTo zoom-animation-origin anchor and review how coordinate positioning is currently explained. Document how to place the (0,0) origin at the page center, including any relevant configuration or API context shown there. Done means a reader can find and follow the explanation without searching elsewhere.

Written by the indexing model from the issue text.