Add Robert Scott to contributors, add documentation

Author: wojtekmaj

package.json

@@ -70,6 +70,10 @@
       "name": "Niklas Närhinen",
       "email": "[email protected]"
     },
+    {
+      "name": "Robert Scott",
+      "email": "[email protected]"
+    },
     {
       "name": "Thomas McCarthy",
       "email": "[email protected]"

src/Page/PageCanvas.jsx

@@ -29,6 +29,11 @@ export class PageCanvasInternal extends PureComponent {
 
   componentWillUnmount() {
     this.cancelRenderingTask();
+
+    /**
+     * Zeroing the width and height cause most browsers to release graphics
+     * resources immediately, which can greatly reduce memory consumption.
+     */
     if (this.canvasLayer) {
       this.canvasLayer.width = 0;
       this.canvasLayer.height = 0;