docs: README broken link

The google-cloud link in the "working with google cloud platform APIs" returns a 404: https://cloud.google.com/nodejs/docs/reference/libraries.

```
### Working with Google Cloud Platform APIs?
If you're working with [Google Cloud Platform][cloudplatform] APIs such as Datastore, Cloud Storage or Pub/Sub, consider using the [`@google-cloud`][googlecloud] client libraries: single purpose idiomatic Node.js clients for Google Cloud Platform services.
```

I'm guessing the link should be: https://cloud.google.com/nodejs/docs/reference

Open the README and find the “Working with Google Cloud Platform APIs” section. Check the current @google-cloud reference URL, update the broken link to the working documentation URL, and verify that the README link no longer returns 404.

Scritto dal modello di indicizzazione a partire dal testo della issue.