docs: Replace image in README with gif

Updated the image in the README to a gif.

Author: phphe

README.md

@@ -1,4 +1,5 @@
-<p align="center"><img src="https://github.com/phphe/he-tree-react/blob/static/cover.jpg?raw=true" width="350" alt="react draggable tree, he-tree-react" /></p>
+
+<p align="center"><img src="https://github.com/user-attachments/assets/96e05767-7643-4ec5-9b43-2c040b42618f" width="350" alt="react draggable tree, he-tree-react" /></p>
 
 # he-tree-react ![GitHub License](https://img.shields.io/github/license/phphe/he-tree-react) ![NPM Version](https://img.shields.io/npm/v/he-tree-react) ![NPM Type Definitions](https://img.shields.io/npm/types/he-tree-react) ![npm bundle size](https://img.shields.io/bundlephobia/minzip/he-tree-react)