Refine LLM settings in env sample file

.env.example

@@ -45,17 +45,21 @@
 # MAX_EMBED_TOKENS=8192
 
 ### LLM Configuration (Use valid host. For local services installed with docker, you can use host.docker.internal)
+LLM_BINDING=ollama
 LLM_MODEL=mistral-nemo:latest
 LLM_BINDING_API_KEY=your_api_key
 ### Ollama example
-LLM_BINDING=ollama
 LLM_BINDING_HOST=http://localhost:11434
 ### OpenAI alike example
 # LLM_BINDING=openai
+# LLM_MODEL=gpt-4o
 # LLM_BINDING_HOST=https://api.openai.com/v1
+# LLM_BINDING_API_KEY=your_api_key
 ### lollms example
 # LLM_BINDING=lollms
+# LLM_MODEL=mistral-nemo:latest
 # LLM_BINDING_HOST=http://localhost:9600
+# LLM_BINDING_API_KEY=your_api_key
 
 ### Embedding Configuration (Use valid host. For local services installed with docker, you can use host.docker.internal)
 EMBEDDING_MODEL=bge-m3:latest