chore: add npm downloads per month badge (#352)

Author: jackwotherspoon

README.md

@@ -8,11 +8,13 @@
 
 [![CI][ci-badge]][ci-build]
 [![npm][npm-badge]][npm-docs]
+[![npm][npm-downloads]][npm-docs]
 
 [ci-badge]: https://github.com/GoogleCloudPlatform/cloud-sql-nodejs-connector/actions/workflows/tests.yml/badge.svg?event=push
 [ci-build]: https://github.com/GoogleCloudPlatform/cloud-sql-nodejs-connector/actions/workflows/tests.yml?query=event%3Apush+branch%3Amain
 [npm-badge]: https://img.shields.io/npm/v/@google-cloud/cloud-sql-connector
 [npm-docs]: https://www.npmjs.com/package/@google-cloud/cloud-sql-connector
+[npm-downloads]: https://img.shields.io/npm/dm/@google-cloud/cloud-sql-connector
 
 The **Cloud SQL Node.js Connector** is a Cloud SQL connector designed for use
 with the Node.js runtime. Using a Cloud SQL connector provides a native
@@ -490,4 +492,4 @@ Apache Version 2.0
 See [LICENSE](./LICENSE)
 
 [credentials-json-file]: https://github.com/googleapis/google-cloud-node#download-your-service-account-credentials-json-file
-[google-auth-creds]: https://cloud.google.com/nodejs/docs/reference/google-auth-library/latest#loading-credentials-from-environment-variables
+[google-auth-creds]: https://cloud.google.com/nodejs/docs/reference/google-auth-library/latest#loading-credentials-from-environment-variables