Update README.md

`PaddleOCRVL()` uses the latest version by default, which is currently `PaddleOCR-VL-1.5`. To explicitly specify an older version, use: `PaddleOCRVL(pipeline_version="v1")`.

README.md

@@ -109,7 +109,7 @@ Python API usage:
 
 ```python
 from paddleocr import PaddleOCRVL
-pipeline = PaddleOCRVL()
+pipeline = PaddleOCRVL(pipeline_version="v1")
 output = pipeline.predict("https://paddle-model-ecology.bj.bcebos.com/paddlex/imgs/demo_image/paddleocr_vl_demo.png")
 for res in output:
     res.print()