Action-91: Write text on fingerprinting risk (ISSUE-109, ISSUE-114), with Nick Doty

Proposed text:

By storing a client-side configurable state and providing functionality to learn about it later, this API may facilitate user fingerprinting and tracking. User agent developers should consider the possibility of fingerprinting during implementation and might consider rate limiting requests or using other heuristics to mitigate fingerprinting risk. User agents should consider clearing stored site-specific exceptions when the user chooses to clear cookies or other client-side state.