docs: constrain demo image width and center for better layout

Images are 830x1051 (portrait), limit to 600px width and center
to prevent excessive vertical scrolling.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: JiaboLi-GitHub

README-CN.md

@@ -12,7 +12,9 @@ renderdoc-mcp 是一个基于 RenderDoc Replay API 的 MCP Server 和 CLI，提
 
 ## 演示
 
-![演示](docs/demo/demo.png)
+<p align="center">
+  <img src="docs/demo/demo.png" alt="演示" width="600">
+</p>
 
 ## 功能概览
 

README.md

@@ -12,7 +12,9 @@ renderdoc-mcp is an MCP server and CLI that wraps the RenderDoc replay API into
 
 ## Demo
 
-![Demo](docs/demo/demo-en.png)
+<p align="center">
+  <img src="docs/demo/demo-en.png" alt="Demo" width="600">
+</p>
 
 ## Features