chore: update readme for v1.0.0 (#213)

This changeset updates the README file to remove mention to being on
preview and adding "Support Policy" and "Release cadence" info.

Also replaces contributing phrase to match the more eloquent version
available in the Python Connector README.

Ref: https://github.com/GoogleCloudPlatform/cloud-sql-python-connector

README.md

@@ -311,8 +311,25 @@ const clientOpts = await connector.getOptions({
   authType: AuthTypes.IAM,
 });
 ```
+## Support policy
 
-## Supported Node.js Versions
+### 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
+supported for 1 year.
+
+**Unsupported** - Any major version that has been deprecated for >=1 year is
+considered unsupported.
+
+### Supported Node.js Versions
 
 Our client libraries follow the
 [Node.js release schedule](https://nodejs.org/en/about/releases/).
@@ -328,18 +345,17 @@ best-efforts basis with the following warnings:
 * Some security patches and features cannot be backported.
 * Dependencies cannot be kept up-to-date.
 
-## Versioning
-
-This library follows [Semantic Versioning](http://semver.org/).
-
-This library is considered to be at **preview**, ready for testing by customers.
+### Release cadence
 
-More Information:
-[Google Cloud Platform Launch Stages](https://cloud.google.com/terms/launch-stages)
+This project aims for a release on at least a monthly basis. If no new features
+or fixes have been added, a new PATCH version with the latest dependencies is
+released.
 
 ## Contributing
 
-Contributions welcome! See the [Contributing Guide](./docs/contributing.md).
+We welcome outside contributions. Please see our
+[Contributing Guide](./docs/contributing.md) for details on how best to
+contribute.
 
 ## License