Update Documentation for Provider arguments in google.md (#1946)

Author: Deriverx2

docs/models/google.md

@@ -107,16 +107,22 @@ agent = Agent(model)
 
 ## Provider Argument
 
-You can provide a custom `Provider` via the `provider` argument, for example to use a pre-initialized `genai.Client` or to customize authentication:
+You can supply a custom `GoogleProvider` instance using the `provider` argument to configure advanced client options, such as setting a custom `base_url`.
+
+This is useful if you're using a custom-compatible endpoint with the Google Generative Language API.
 
 ```python
 from google import genai
+from google.genai.types import HttpOptions
 
 from pydantic_ai import Agent
 from pydantic_ai.models.google import GoogleModel
 from pydantic_ai.providers.google import GoogleProvider
 
-client = genai.Client()
+client = genai.Client(
+    api_key='gemini-custom-api-key',
+    http_options=HttpOptions(base_url='gemini-custom-base-url')
+    )
 provider = GoogleProvider(client=client)
 model = GoogleModel('gemini-1.5-flash', provider=provider)
 agent = Agent(model)