Using simpler sentence from code review.

Co-authored-by: Ted Thibodeau Jr <tthibodeau@openlinksw.com>

index.html

@@ -542,10 +542,9 @@ <h3>Ecosystem Overview</h3>
 specification. Specifically, the relevant normative "MUST" statements in
 Sections [[[#basic-concepts]]], [[[#advanced-concepts]]], and
 [[[#syntaxes]]] of this document MUST be enforced.
-A conforming document MUST be either a [=verifiable credential=] with a
-serialization identified by the `application/vc` media type or a
-[=verifiable presentation=] with a serialization identified by
-`application/vp`. A conforming document MUST be
+A conforming document MUST be either a [=verifiable credential=]
+with a media type of `application/vc` or a [=verifiable presentation=]
+with a media type of `application/vp`. A conforming document MUST be
 secured by at least one securing mechanism as described in Section
 [[[#securing-mechanisms]]].
  </p>