Update model reference for Ollama

Author: danbarr

docs/partials/_aider-providers.mdx

@@ -99,7 +99,7 @@ Restart your shell after running `setx`.
 Then run Aider:
 
 ```bash
-aider --model ollama/<MODEL_NAME>
+aider --model ollama_chat/<MODEL_NAME>
 ```
 
 Replace `<MODEL_NAME>` with the name of a coding model you have installed