chore: update README with py3.9 and 3.10 test status (GoogleCloudPlatform#7591)

## Description

Adds 3.9 and 3.10 test status to the README page.

## Checklist
- [x] I have followed [Sample Guidelines from AUTHORING_GUIDE.MD](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/main/AUTHORING_GUIDE.md)
- [x] README is updated to include [all relevant information](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/main/AUTHORING_GUIDE.md#readme-file)
- [x] **Tests** pass:   `nox -s py-3.6` (see [Test Environment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/main/AUTHORING_GUIDE.md#test-environment-setup))
- [x] **Lint** pass:   `nox -s lint` (see [Test Environment Setup](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/main/AUTHORING_GUIDE.md#test-environment-setup))
- [x] Please **merge** this PR for me once it is approved.

Author: dandhlee

README.md

@@ -2,7 +2,7 @@
 
 Python samples for [Google Cloud Platform products][cloud].
 
-[![Build Status][py-2.7-shield]][py-2.7-link] [![Build Status][py-3.6-shield]][py-3.6-link] [![Build Status][py-3.7-shield]][py-3.7-link] [![Build Status][py-3.8-shield]][py-3.8-link]
+[![Build Status][py-2.7-shield]][py-2.7-link] [![Build Status][py-3.6-shield]][py-3.6-link] [![Build Status][py-3.7-shield]][py-3.7-link] [![Build Status][py-3.8-shield]][py-3.8-link] [![Build Status][py-3.9-shield]][py-3.9-link] [![Build Status][py-3.10-shield]][py-3.10-link]
 
 ## Setup
 
@@ -71,3 +71,7 @@ Contributions welcome! See the [Contributing Guide](CONTRIBUTING.md).
 [py-3.7-link]: https://storage.googleapis.com/cloud-devrel-public/python-docs-samples/badges/py-3.7.html
 [py-3.8-shield]: https://storage.googleapis.com/cloud-devrel-public/python-docs-samples/badges/py-3.8.svg
 [py-3.8-link]: https://storage.googleapis.com/cloud-devrel-public/python-docs-samples/badges/py-3.8.html
+[py-3.9-shield]: https://storage.googleapis.com/cloud-devrel-public/python-docs-samples/badges/py-3.9.svg
+[py-3.9-link]: https://storage.googleapis.com/cloud-devrel-public/python-docs-samples/badges/py-3.9.html
+[py-3.10-shield]: https://storage.googleapis.com/cloud-devrel-public/python-docs-samples/badges/py-310.svg
+[py-3.10-link]: https://storage.googleapis.com/cloud-devrel-public/python-docs-samples/badges/py-3.10.html