Add Sky docs (#1006)

types/three/examples/jsm/objects/Sky.d.ts

@@ -1,6 +1,24 @@
 import { BoxGeometry, Mesh, ShaderMaterial } from "three";
 
+/**
+ * {@link Sky} creates a ready to go sky environment for your scenes.
+ *
+ * @example
+ * const sky = new Sky();
+ * sky.scale.setScalar( 450000 );
+ *
+ * const phi = MathUtils.degToRad( 90 );
+ * const theta = MathUtils.degToRad( 180 );
+ * const sunPosition = new Vector3().setFromSphericalCoords( 1, phi, theta );
+ *
+ * sky.material.uniforms.sunPosition.value = sunPosition;
+ *
+ * scene.add( sky );
+ */
 export class Sky extends Mesh {
+    /**
+     * Create a new {@link Sky} instance.
+     */
     constructor();
 
     geometry: BoxGeometry;