Add Social IdP Example

[ZLevine]

Thanks for the great starter! It's been a great reference.

One thing I think would be a great addition is a Facebook/Google auth login example. Most examples out there use the Authenticator high order component from aws-amplify-react, which this starter site stays away from.

[swaminator]

@dabit3 created this awesome post: https://dev.to/dabit3/the-complete-guide-to-user-authentication-with-the-amplify-framework-2inh. Hope it helps!