New section on Security and Privacy considerations on Discovery

[mlagally]

need to mention DoS, ...

Will be done together when the discovery section is being added.

[mmccool]

Hmm... don't currently do this in my discovery PR, let me add...

[mmccool]

Should probably consolidate this with an overall review of security and privacy considerations. Detailed discovery considerations should probably go in the discovery spec so we'll also need to discuss what goes where. Anyway, here is an issue in the TD spec for this review, I am planning to create similar issues in each deliverable's repo and discuss these in the security calls this month: w3c/wot-thing-description#1348

[mmccool]

I have created a new issue to do a general review of S&P considerations for architecture (as we have just completed for Discovery and TD specs): #726.

For DDoS in particular, I just finished adding a detailed Security consideration to Discovery and don't want to duplicate that in Architecture. However, a general statement in Architecture about "discouraging DDoS" might be useful.

Propose closing this issue and consolidating this discussion under Issue #726.