docs(readme): add section on determining installed version (#1697)

README.md

@@ -507,6 +507,17 @@ We take backwards-compatibility seriously and work hard to ensure you can rely o
 
 We are keen for your feedback; please open an [issue](https://github.com/openai/openai-python/issues) with questions, bugs, or suggestions.
 
+### Determining the installed version
+
+If you've upgraded to the latest version but aren't seeing any new features you were expecting then your python environment is likely still using an older version.
+
+You can determine the version that is being used at runtime with:
+
+```py
+import openai
+print(openai.__version__)
+```
+
 ## Requirements
 
 Python 3.7 or higher.