Update titles for media type and structured suffix registration per @TallTed's suggestion.

Author: gkellogg

index.html

@@ -13454,7 +13454,7 @@ <h2>IANA Considerations</h2>
     Group (IESG) for review, approval, and registration with IANA.</p>
 
   <section id="application-ld-json">
-    <h3>application/ld+json</h3>
+    <h3>Media Type Registration: `application/ld+json`</h3>
     <dl>
       <dt>Type name:</dt>
       <dd>application</dd>
@@ -13611,7 +13611,7 @@ <h3>Examples</h3>
     </section>
   </section>
   <section id="structured-extension-ld-json">
-    <h3>+ld+json</h3>
+    <h3>Structured Suffix Registration: `+ld+json`</h3>
 
     <p>This section will be submitted to the Internet Engineering Steering
     Group (IESG) for review, approval, and registration with IANA.</p>