Update version compatibility in README

Author: henribru

README.md

@@ -3,7 +3,7 @@
 [![PyPI version](https://badge.fury.io/py/google-ads-stubs.svg)](https://badge.fury.io/py/google-ads-stubs)
 
 This package provides type stubs for the [Google Ads API Client Library for Python](https://github.com/googleads/google-ads-python). 
-It's currently compatible with v20.0.0 of this library. It allows you to type check usage of the library with e.g. [mypy](http://mypy-lang.org/) and will also improve autocomplete in many editors.
+It's currently compatible with v21.1.0 of this library. It allows you to type check usage of the library with e.g. [mypy](http://mypy-lang.org/) and will also improve autocomplete in many editors.
 
 **This is in no way affiliated with Google.**