📚 docs(watermark): 更新水印提取文档示例/Updated watermark extraction document example

[Radium-bit]

• 修正wm_shape参数说明：文档示例中，将 wm_shape 参数的传递方式从 WaterMark 类初始化时调整为 extract 方法调用时传入，以符合最新代码逻辑
• 更新示例文件名：将英文示例中水印图片的文件名从 打上水印的图.png 更新为 embedded.png
• Corrected the wm_shape parameter description: In the document example, the wm_shape parameter was passed from the WaterMark class initialization to the extract method call to conform to the latest code logic
• Updated the example file name: Updated the watermark image file name in the English example from watermarked.png to embedded.png