LinkedIn requires the Oauth2 URL to be set

Error from LinkedIn following the instructions:

```
invalid redirect_uri. This value must match a URL registered with the API Key.
```

I had to set the OAuth 2.0 Redirect URLs to:
https://example.com/path-to-opauth/linkedin/oauth2callback

I suggest that you update the README and adjust the permissions for your app (your demo generates the error too).
