Update README_PYPI.md

Author: rybakov-ks

README_PYPI.md

@@ -52,4 +52,10 @@ Open in browser: http://127.0.0.1:8000
 
 You can specify the port if necessary:
 ```python
-ParticleAnalyzer run --port 5000
+ParticleAnalyzer run --port 5000
+```
+
+Launch with LLM support ([OpenRouter](https://openrouter.ai/settings/keys) API key required):
+```python
+ParticleAnalyzer run --port 5000 --api-key YOUR_OPENROUTER_API_KEY
+```