Add a link to web-platform-tests to the top of the spec
Many other specs that have something similar:
https://fetch.spec.whatwg.org/
https://w3c.github.io/IndexedDB/
https://notifications.spec.whatwg.org/
https://w3c.github.io/ServiceWorker/
https://webaudio.github.io/web-audio-api/
https://xhr.spec.whatwg.org/