Tutorial adds authentication, but does not secure the API

**Page**: [`/start/getting-started/data-model/q/integration/[integration]`](https://docs.amplify.aws/start/getting-started/data-model/q/integration/react/#connect-frontend-to-api)

**Feedback**:

This tutorial appears to have a rather significant security issue in that the "Add authentication" section of the tutorial gives the false appearance of securing the back-end, but rather only hides portions of the UI from unauthenticated users.

Please add a section called "Securing the API" which goes through the process of configuring the API (adding @auth to schema.graphql?) and passing the tokens to the GraphQL calls in addTodo and fetchTodos.