Update README.

Runtime/Plugins/platform/webgl/UIWidgetsCanvasDevicePixelRatio.jslib

 mergeInto(LibraryManager.library, {
     JS_SystemInfo_GetWidth: function () {
+        //////////// Modification Start ////////////////////
+        //////////// Modification End ////////////////////
+        //////////// Modification Start ////////////////////
+        //////////// Modification End ////////////////////
+        //////////// Modification Start ////////////////////
+        //////////// Modification End ////////////////////
+        //////////// Modification Start ////////////////////
+        //////////// Modification End ////////////////////
     },
     $Browser : {
         mainLoop: {