Add arch diagram section

Author: pamelafox

README.md

@@ -40,6 +40,10 @@ so that you can use the OpenAI API SDKs with keyless (Entra) authentication.
 * Deploys a gpt-3.5 model by default, but you can modify the [Bicep template](infra/main.bicep) to deploy other models
 * Example script uses the [openai](https://pypi.org/project/openai/) Python package to make a request to the Azure OpenAI API
 
+### Architecture diagram
+
+![Architecture diagram: Microsoft Entra managed identity connecting to Azure AI services](./diagram.png)
+
 ## Getting started
 
 You have a few options for getting started with this template.