Update README with instructions for running OpenAI tests

Author: donald-pinckney

README.md

@@ -90,3 +90,7 @@ Some examples require extra dependencies. See each sample's directory for specif
 To run the tests:
 
     uv run poe test
+
+By default, this won't run the OpenAI SDK sample tests. To run those, set your `OPENAI_API_KEY` in your environment, and run:
+
+    uv run poe test tests/openai_agents