Refer to the threat model in the Use Cases document. Fix #251.

Author: msporny

index.html

@@ -675,6 +675,12 @@ <h1>Trust Model</h1>
 <a>relying party</a>, a more flexible and dynamic trust model is created
 such that market competition and customer choice is increased.
       </p>
+
+      <p>
+Readers that would like to learn more about how this trust model interacts
+with various threat models studied by the Working Group are urged to read
+the Verifiable Credentials Use Cases Document [[VC-USECASES]].
+      </p>
     </section>
 
     <section>