RUpdated reveal-when-loaded to reveal in docs (google#550)

README.md

@@ -144,7 +144,7 @@ Safari has support for something like the WebXR Device and Hit Test APIs.
 
 Models are often large, so especially on pages with large numbers of them it
 may be desirable to load them after user action. Three parameters -
-*`poster`*, *`preload`*, and *`reveal-when-loaded`* - control the loading
+*`poster`*, *`preload`*, and *`reveal`* - control the loading
 behavior.
 
 Four configuration options are available:

index.html

@@ -199,8 +199,14 @@ <h3 class="grouping-title">Attributes</h3>
               <p>When poster is also enabled, the model will be downloaded before user action. See <a href="https://github.com/GoogleWebComponents/model-viewer#on-loading">On Loading</a> for more information.</p>
             </li>
             <li>
-              <div>reveal-when-loaded</div>
-              <p>When poster and preload are specified, hide the poster and show the model once the model has been loaded. See <a href="https://github.com/GoogleWebComponents/model-viewer#on-loading">On Loading</a> for more information.</p>
+              <div>reveal</div>
+              <p>This attribute controls whether or not the model should be
+            automatically revealed when loaded. It currently supports two
+            values: "auto" and "interaction". If reveal is set to "interaction",
+            &lt;model-viewer&gt; will wait until the user interacts with the
+            poster before loading and revealing the model. Otherwise, the model
+            will be revealed as soon as it is done loading and rendering.
+            Defaults to "auto".</p>
             </li>
             <li>
               <div>shadow-intensity</div>