document outputEncoding override behavior.

docs/api/en/renderers/WebGLRenderer.html

@@ -166,6 +166,7 @@
 
 		<h3>[property:number outputEncoding]</h3>
 		<p>Defines the output encoding of the renderer. Default is [page:Textures THREE.LinearEncoding].</p>
+		<p>If a render target has been set using [page:WebGLRenderer.setRenderTarget .setRenderTarget] then renderTarget.texture.encoding will be used instead.</p>
 		<p>See the [page:Textures texture constants] page for details of other formats.</p>
 
 		<h3>[property:Object info]</h3>