Add nonce parameter to example Settings request

[iandunn]

This endpoint requires authorization from a user with manage_options, so the previous example would never work.

The domain changed to encourage users to test against their own sites, since they won't have valid nonces for demo.wp-api.org.

[TimothyBJacobs]

This file is automatically generated by this twig template: https://github.com/WP-API/docs/blob/master/bin/templates/reference-parts/examples/update-post-curl.html

I don't think we have a great way right now to only apply changes for certain resources.

[kadamwhite]

I'm going to close this, not because it's not valid but because our current scheme for documentation generation doesn't give us an escape hatch to note these sorts of things. I'll convert this to an issue to revisit the templating in the future.