[worklets] Add renderWorklet as attribute to window for now.

Author: bfgeek

worklets/Overview.bs

@@ -271,6 +271,25 @@ it must run the following steps:
 
 Note: It is up to the user agent to select a appropriate {{WorkletGlobalScope}} to invoke the method in.
 
+Rendering Worklet {#rendering-worklet}
+--------------------------------------
+
+The {{renderWorklet}} attribute allows access to the {{Worklet}} responsible for all the classes
+which are related to rendering.
+
+<pre class='idl'>
+partial interface Window {
+    [SameObject] readonly attribute Worklet renderWorklet;
+};
+</pre>
+
+The {{RenderWorkletGlobalScope}} is the global execution context of the {{renderWorklet}}.
+
+<pre class='idl'>
+interface RenderWorkletGlobalScope : WorkletGlobalScope {
+};
+</pre>
+
 Examples {#examples}
 ====================