ACTION-420: Propose non-normative text on use of Disregard signal

There are a variety of situations where a service can not fulfill the request not to be tracked. It simply has to turn the mechanism off. But how to tell the user? One of the core principles in modern legal systems is the freedom to contract. A user requesting not to be tracked is just a request, not an agreement yet. By confirming or infirming, the service is binding itself to the rules as set forth in this specification. The "D" signal on return of a GET request tells a user agent that its DNT:1 signal will not be respected for this particular request.