add know issues

README.md

@@ -93,6 +93,18 @@ print(f"Similarity: {similarity.item():.4f}")
 - Cross-lingual retrieval
 - Text classification with embeddings
 
+## Known Issues
+
+When encoding documents without any instruction prefix, you may encounter unexpected behavior due to an [upstream issue in Qwen3-Embedding](https://huggingface.co/Qwen/Qwen3-Embedding-8B/discussions/21). To avoid this issue, we recommend adding `"- "` (dash followed by space) at the beginning of your text when encoding documents:
+
+```python
+# Recommended: Add "- " prefix for document encoding
+documents = ["- " + doc for doc in documents]
+embeddings = model.encode(documents)
+```
+
+This workaround ensures consistent and expected embedding behavior.
+
 ## Limitations
 
 - Performance may vary across different domains and languages