Fix missing comma in README code example (#1000)

The previous version of the README contained a code example with a missing comma, which could lead to syntax errors. This commit corrects that issue by adding the missing comma.

README.md

@@ -475,7 +475,7 @@ from openai import AzureOpenAI
 # gets the API Key from environment variable AZURE_OPENAI_API_KEY
 client = AzureOpenAI(
     # https://learn.microsoft.com/en-us/azure/ai-services/openai/reference#rest-api-versioning
-    api_version="2023-07-01-preview"
+    api_version="2023-07-01-preview",
     # https://learn.microsoft.com/en-us/azure/cognitive-services/openai/how-to/create-resource?pivots=web-portal#create-a-resource
     azure_endpoint="https://example-endpoint.openai.azure.com",
 )