Update README.md

```
processing_qwen2_vl.py", line 140, in __call__
text[i] = text[i].replace("<|placeholder|>", "<|image_pad|>")
AttributeError: 'list' object has no attribute 'replace'
```

processor expects `str` instead of `token_ids`

README.md

@@ -197,7 +197,7 @@ conversation = [
 
 
 # Preprocess the inputs
-text_prompt = processor.apply_chat_template(conversation, add_generation_prompt=True)
+text_prompt = processor.apply_chat_template(conversation, tokenize=False, add_generation_prompt=True)
 # Excepted output: '<|im_start|>system\nYou are a helpful assistant.<|im_end|>\n<|im_start|>user\n<|vision_start|><|image_pad|><|vision_end|>Describe this image.<|im_end|>\n<|im_start|>assistant\n'
 
 inputs = processor(