fix wrong image path for architecture (#4471)

* fix wrong image path for architecture

the original image path "https://github.com/vesoft-inc/nebula-docs/raw/master/images/Nebula%20Arch.png" is outdated and cannot be loaded by browsers.
I used the image path for architecture from English README as a replacement.

* change the architecture image path with given url

#4471 (comment)

Co-authored-by: Sophie <84560950+Sophie-Xie@users.noreply.github.com>

README-CN.md

@@ -77,7 +77,7 @@ Nebula Graph 1.x 后续不再进行功能的更新，请升级到2.0版本中。
 
 ## Nebula Graph 产品架构图
 
-![image](https://github.com/vesoft-inc/nebula-docs/raw/master/images/Nebula%20Arch.png)
+![image](https://docs-cdn.nebula-graph.com.cn/figures/nebula-graph-architecture_3.png)
 
 ## 如何贡献