chore(readme): update badges

Author: stainless-app[bot]

README.md

@@ -1,5 +1,5 @@
 # Codex SDK
 
-[![PyPI version](https://img.shields.io/pypi/v/codex-sdk.svg)](https://pypi.org/project/codex-sdk/)
+[![PyPI version](<https://img.shields.io/pypi/v/codex-sdk.svg?label=pypi%20(stable)>)](https://pypi.org/project/codex-sdk/)
 
 This library is not meant to be used directly. Refer to https://pypi.org/project/cleanlab-codex/ instead.