Add docs and TS declaration for .fromEquirectangularTexture().

docs/api/en/renderers/WebGLRenderTargetCube.html

@@ -57,6 +57,14 @@
 
 		<h3>See [page:WebGLRenderTarget] for inherited methods</h3>
 
+		<h3>[method:WebGLRenderTargetCube fromEquirectangularTexture]( [param:WebGLRenderer renderer], [param:Texture texture] )</h3>
+		<p>
+			[page:WebGLRenderer renderer] — the renderer.<br/>
+			[page:Texture texture] — the equirectangular texture.
+		</p>
+		<p>
+			Use this method if you want to convert an equirectangular panorama to the cubemap format.
+		</p>
 
 		<h2>Source</h2>
 

docs/api/zh/renderers/WebGLRenderTargetCube.html

@@ -54,6 +54,14 @@
 
 		<h3>继承方法，请参阅[page:WebGLRenderTarget]</h3>
 
+		<h3>[method:WebGLRenderTargetCube fromEquirectangularTexture]( [param:WebGLRenderer renderer], [param:Texture texture] )</h3>
+		<p>
+			[page:WebGLRenderer renderer] — the renderer.<br/>
+			[page:Texture texture] — the equirectangular texture.
+		</p>
+		<p>
+			Use this method if you want to convert an equirectangular panorama to the cubemap format.
+		</p>
 
 		<h2>源码</h2>
 

src/renderers/WebGLRenderTargetCube.d.ts

@@ -1,7 +1,6 @@
-import {
-	WebGLRenderTargetOptions,
-	WebGLRenderTarget,
-} from './WebGLRenderTarget';
+import { WebGLRenderTargetOptions, WebGLRenderTarget } from './WebGLRenderTarget';
+import { WebGLRenderer } from './WebGLRenderer';
+import { Texture } from './../textures/Texture';
 
 export class WebGLRenderTargetCube extends WebGLRenderTarget {
 
@@ -11,4 +10,6 @@ export class WebGLRenderTargetCube extends WebGLRenderTarget {
 		options?: WebGLRenderTargetOptions
 	);
 
+	fromEquirectangularTexture( renderer: WebGLRenderer, texture: Texture ): this;
+
 }