chore(readme): update badges

Author: stainless-app[bot]

README.md

@@ -1,6 +1,6 @@
 # Anthropic Python API library
 
-[![PyPI version](https://img.shields.io/pypi/v/anthropic.svg)](https://pypi.org/project/anthropic/)
+[![PyPI version](<https://img.shields.io/pypi/v/anthropic.svg?label=pypi%20(stable)>)](https://pypi.org/project/anthropic/)
 
 The Anthropic Python library provides convenient access to the Anthropic REST API from any Python 3.8+
 application. It includes type definitions for all request params and response fields,