docs: Add Support policy to README (#583)

Co-authored-by: Shubha Rajan <[email protected]>

README.md

@@ -73,3 +73,23 @@ Here are some troubleshooting tips to resolve common issues that come up when us
 
 [ci-badge-java-8]: https://storage.googleapis.com/cloud-devrel-public/cloud-sql-connectors/java/java8_linux.svg
 [ci-badge-java-11]: https://storage.googleapis.com/cloud-devrel-public/cloud-sql-connectors/java/java11_linux.svg
+
+## Support policy
+
+### Major version lifecycle
+This project uses [semantic versioning](https://semver.org/), and uses the
+following lifecycle regarding support for a major version:
+
+**Active** - Active versions get all new features and security fixes (that
+wouldn’t otherwise introduce a breaking change). New major versions are
+guaranteed to be "active" for a minimum of 1 year.
+**Deprecated** - Deprecated versions continue to receive security and critical
+bug fixes, but do not receive new features. Deprecated versions will be publicly
+supported for 1 year.
+**Unsupported** - Any major version that has been deprecated for >=1 year is
+considered publicly unsupported.
+
+### Release cadence
+This project aims for a minimum monthly release cadence. If no new
+features or fixes have been added, a new PATCH version with the latest
+dependencies is released.