Correct clarification for data: URIs (#387)

Closes #386

index.html

@@ -322,11 +322,10 @@ <h3>
           <li>If an HTML <code>IMG</code> element has a <code><a href=
           "https://tools.ietf.org/html/rfc2397">data: URI</a></code> as its
           source [[RFC2397]], then this resource will not be included as a <a>
-            PerformanceResourceTiming</a> object in the <a data-cite=
-            "PERFORMANCE-TIMELINE-2#performance-timeline">Performance
-            Timeline</a>. By definition <code><a href=
-            "https://tools.ietf.org/html/rfc2397">data: URI</a></code> contains
-            embedded data and does not require a [=fetch=].
+          PerformanceResourceTiming</a> object in the <a data-cite=
+          "PERFORMANCE-TIMELINE-2#performance-timeline">Performance
+          Timeline</a>. <a>PerformanceResourceTiming</a> entries are only reported for
+          [=http(s) scheme|http(s)=] resources.
           </li>
           <li>If a resource <a data-cite="FETCH#concept-fetch">fetch</a> was
           aborted due to a networking error (e.g. DNS, TCP, or TLS error), then