Update api.md (#2196)

### What problem does this PR solve?


### Type of change

- [x] Documentation Update

---------

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
Co-authored-by: writinwaters <93570324+writinwaters@users.noreply.github.com>

docs/references/api.md

@@ -398,7 +398,43 @@ This method uploads a specific file to a specified knowledge base.
     "retmsg": "success"
 }
 ```
-
+### Demo for Upload File(Python) 
+
+```python
+# upload_to_kb.py  
+import requests
+
+
+def upload_file_to_kb(file_path, kb_name, token='ragflow-xxxxxxxxxxxxx', parser_id='naive'):
+    """  
+    Uploads a file to a knowledge base.  
+
+    Args:  
+    - file_path: Path to the file to upload.  
+    - kb_name: Name of the target knowledge base.  
+    - parser_id: ID of the chosen file parser (defaults to 'naive').  
+    - token: API token for authentication.  
+    """
+    url = 'http://127.0.0.1/v1/api/document/upload'  # Replace with your actual API URL  
+    files = {'file': open(file_path, 'rb')}  # The file to upload  
+    data = {'kb_name': kb_name, 'parser_id': parser_id, 'run': '1'}  # Additional form data  
+    headers = {'Authorization': f'Bearer {token}'}  # Replace with your actual Bearer token  
+
+    response = requests.post(url, files=files, data=data, headers=headers)
+
+    if response.status_code == 200:
+        print("File uploaded successfully:", response.json())
+    else:
+        print("Failed to upload file:", response.status_code, response.text)
+
+file_to_upload = './ai_intro.pdf'  # For example: './documents/report.pdf'  
+knowledge_base_name = 'AI_knowledge_base'
+# Assume you have already obtained your token and set it here  
+token = 'ragflow-xxxxxxxxxxxxx'
+
+# Call the function to upload the file  
+upload_file_to_kb(file_to_upload, knowledge_base_name, token=token)
+```
 ## Get document chunks
 
 This method retrieves the chunks of a specific document by `doc_name` or `doc_id`.