allow environment variable for BASE_DIR models (#14678)

* allow environment variable for BASE_DIR models

* add doc for environment variable PADDLE_OCR_BASE_DIR

* fix code style error

docs/quick_start.en.md

@@ -24,6 +24,10 @@ hide:
     python -m pip install paddlepaddle-gpu==3.0.0rc1 -i https://www.paddlepaddle.org.cn/packages/stable/cu118/
     ```
 
+You can customize the storage location for OCR models by setting the environment variable `PADDLE_OCR_BASE_DIR`. If this variable is not set, the models will be downloaded to the following default locations:
+- On Linux/macOS: `${HOME}/.paddleocr`
+- On Windows: `C:\Users\{username}\.paddleocr`
+
 ### Use by code
 
 === "Detection + Classification + Recognition"

paddleocr.py

@@ -85,7 +85,7 @@ __all__ = [
 
 SUPPORT_DET_MODEL = ["DB"]
 SUPPORT_REC_MODEL = ["CRNN", "SVTR_LCNet"]
-BASE_DIR = os.path.expanduser("~/.paddleocr/")
+BASE_DIR = os.environ.get("PADDLE_OCR_BASE_DIR", os.path.expanduser("~/.paddleocr/"))
 
 DEFAULT_OCR_MODEL_VERSION = "PP-OCRv4"
 SUPPORT_OCR_MODEL_VERSION = ["PP-OCR", "PP-OCRv2", "PP-OCRv3", "PP-OCRv4"]