Update README.md

README.md

@@ -23,7 +23,7 @@ To install the pettingzoo base library, use `pip install pettingzoo`.
 
 This does not include dependencies for all families of environments (there's a massive number, and some can be problematic to install on certain systems). You can install these dependencies for one family like `pip install pettingzoo[atari]` or use `pip install pettingzoo[all]` to install all dependencies.
 
-We support Python 3.6, 3.7 and 3.8 on Linux and macOS. We will accept PRs related to Windows, but do not officially support it.
+We support Python 3.6, 3.7, 3.8 and 3.9 on Linux and macOS. We will accept PRs related to Windows, but do not officially support it.
 
 ## API