docs: update banner

README.md

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 [中文版](README_CN.md)
 
-![preview](docs/images/preview.png)
+<img src="docs/images/ncform-banner.gif" alt="preview" style="max-width:100%;">
 
 ncform, a nice form development way that generates form UIs and their interactions with just configuration.
 

README_CN.md

@@ -9,7 +9,7 @@
 
 [English Version](README.md)
 
-![preview](docs/images/preview.png)
+<img src="docs/images/ncform-banner.gif" alt="preview" style="max-width:100%;">
 
 ncform，一种令人愉悦的表单开发方式，仅需配置即可生成表单UI及其交互行为。