Updated OpenAI configuration and documentation.

- Added OpenAI alike example in .env.example
- Updated README for OpenAI alike server
- Modified API key handling in lightrag_server.py

.env.example

@@ -12,6 +12,12 @@ LLM_BINDING=ollama
 LLM_BINDING_HOST=http://host.docker.internal:11434
 LLM_MODEL=mistral-nemo:latest
 
+# OpenAI alike example
+# LLM_BINDING=openai
+# LLM_BINDING_HOST=https://localhost:11434/api
+# LLM_MODEL=deepseek-chat
+# LLM_BINDING_API_KEY=your_api_key
+
 # Lollms example
 # LLM_BINDING=lollms
 # LLM_BINDING_HOST=http://host.docker.internal:9600