Change "registry" to system.

index.html

@@ -288,9 +288,8 @@ <h1>
     </p>
 
     <p>
-This design eliminates dependence on centralized registries
-for identifier and key management, which is the
-standard in hierarchical <a
+This design eliminates dependence on centralized identifier and key management
+systems, which is the standard in hierarchical <a
 href="https://en.wikipedia.org/wiki/Public_key_infrastructure">
   PKI (public key infrastructure</a>).
 In cases where the <a>DID registry</a> is a <a>distributed ledger</a>, each