docs: add scope when loading credentials from file in google (#1850)

Author: Kludex

docs/models/google.md

@@ -80,7 +80,10 @@ from pydantic_ai import Agent
 from pydantic_ai.models.google import GoogleModel
 from pydantic_ai.providers.google import GoogleProvider
 
-credentials = service_account.Credentials.from_service_account_file('path/to/service-account.json')
+credentials = service_account.Credentials.from_service_account_file(
+    'path/to/service-account.json',
+    scopes=['https://www.googleapis.com/auth/cloud-platform'],
+)
 provider = GoogleProvider(credentials=credentials)
 model = GoogleModel('gemini-1.5-flash', provider=provider)
 agent = Agent(model)