Fixed one id in example that wasn't an urn.

index.html

@@ -4489,8 +4489,8 @@ <h2>Understanding Proof Sets and Proof Chains</h2>
 Now, when the CEO validates the received the verifiable credential with the above <em>proof
 chain</em>, they will check that the CFO signed based on the signature of the
 VP of Engineering. First, they will check the proof/signature with
-`id = 0` against the public key of the VP of Engineering. Note that
-this proof/signature is over the original document. 
+`id = urn:proof-0` against the public key of the VP of Engineering. Note that
+this proof/signature is over the original document.
       </p>
       <p>
 Next, the CEO will check the proof/signature `id = "urn:proof-1"` against the