Add link to example.

README.md

@@ -1,6 +1,6 @@
 # Puppet::ResourceApi [![Build Status](https://travis-ci.org/puppetlabs/puppet-resource_api.svg?branch=master)](https://travis-ci.org/puppetlabs/puppet-resource_api) [![Appveyor Build Status](https://ci.appveyor.com/api/projects/status/qvor6rkh0d1e4suc?svg=true)](https://ci.appveyor.com/project/puppetlabs/puppet-resource-api) [![Coverage Status](https://coveralls.io/repos/github/puppetlabs/puppet-resource_api/badge.svg?branch=master)](https://coveralls.io/github/puppetlabs/puppet-resource_api?branch=master)
 
-This is an implementation of the [Resource API](https://github.com/DavidS/puppet-specifications/blob/resourceapi/language/resource-api/README.md) proposal.
+This is an implementation of the [Resource API](https://github.com/DavidS/puppet-specifications/blob/resourceapi/language/resource-api/README.md) proposal. Find a working example of a new-style provider in the [experimental puppetlabs-apt branch](https://github.com/DavidS/puppetlabs-apt/blob/resource-api-experiments/lib/puppet/provider/apt_key2/apt_key2.rb). There is also the corresponding [type](https://github.com/DavidS/puppetlabs-apt/blob/resource-api-experiments/lib/puppet/type/apt_key2.rb), and [new unit tests](https://github.com/DavidS/puppetlabs-apt/blob/resource-api-experiments/spec/unit/puppet/provider/apt_key2/apt_key2_spec.rb) for 100% coverage.
 
 ## Installation