Add reference to living threat model document

[msporny]

From the SING review:

Threat model – acknowledged WG efforts and suggested referencing a living, community-maintained model.
Add a short pointer section, e.g., “Threat Modeling Resources for DID Deployments,” linking to the evolving model.
Encourage iterative contributions and updates aligned with new use cases. This improves implementer readiness and continuity beyond the current charter.

[msporny]

A PR should be raised that points to a WG maintained threat model that is a living document.

[msporny]

I have created a DID Threat Model document here:

https://msporny.github.io/did-threat-model/

WARNING: As an experiment, I used an LLM to generate the vast majority of the content (diagrams, components, threats, etc.). I have done a cursory review of the document, spot checking certain parts of it that seemed relevant, and while there are some things that could use improvement, it feels like a good first draft (that we will need to iterate on heavily). I realize this raises a whole bunch of concerns around the use of AI and LLMs in security work, but let's talk through those concerns because I see AI/LLMs as potentially helpful in identifying potential security vulnerabilities that are then vetted by humans.

This is a request for a WG discussion about adopting this work and citing it as a living threat model document.

/cc @wip-abramson @ottomorac @jandrieu @dmitrizagidulin @swcurran