Docs: Improved animate() description.

docs/api/renderers/WebGLRenderer.html

@@ -287,8 +287,8 @@
 		</div>
 
 		<h3>[method:null animate]( [param:Function callback] )</h3>
-		<div>[page:Function callback] — (optional) If specified, the function will be called every available frame. If left empty it will stop any already ongoing animation started by this function.</div>
-		<div>A build in function that can be used instead of [link:https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame requestAnimationFrame].</div>
+		<div>[page:Function callback] — The function will be called every available frame. If `null` is passed it will stop any already ongoing animation.</div>
+		<div>A build in function that can be used instead of [link:https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame requestAnimationFrame]. For WebVR projects this function must be used.</div>
 
 		<h3>[method:null clear]( [param:Boolean color], [param:Boolean depth], [param:Boolean stencil] )</h3>
 		<div>