Updated documentation for pip install in zsh

Fixes jupyterlab#1209

Updated documentation to handle installation using `zsh` on Macs, which is now the default shell.

packages/jupyter-ai-magics/jupyter_ai_magics/partner_providers/openrouter.py

@@ -38,7 +38,7 @@ def __init__(self, **kwargs):
         )
 
         super().__init__(
-            openai_api_key=openrouter_api_key,
+            openai_api_key=kwargs.pop("openrouter_api_key"),
             openai_api_base=openrouter_api_base,
             **kwargs,
         )