docs(usage): update Reader examples

Author: floryst

usage/src/App.jsx

@@ -6,7 +6,7 @@ import useQueryString from './useQueryString';
 
 const demos = new Map([
   ['Geometry/Picking', lazy(() => import('./Geometry/Picking'))],
-  // ['Geometry/OBJViewer', lazy(() => import('./Geometry/OBJViewer'))],
+  ['Geometry/OBJViewer', lazy(() => import('./Geometry/OBJViewer'))],
   // ['Geometry/PointCloud', lazy(() => import('./Geometry/PointCloud'))],
   ['Geometry/PolyDataViewer', lazy(() => import('./Geometry/PolyDataViewer'))],
   [
@@ -19,7 +19,7 @@ const demos = new Map([
   // ],
   ['Geometry/SourceViewer', lazy(() => import('./Geometry/SourceViewer'))],
   // ['Geometry/Glyph', lazy(() => import('./Geometry/Glyph'))],
-  // ['Geometry/CutterExample', lazy(() => import('./Geometry/CutterExample'))],
+  ['Geometry/CutterExample', lazy(() => import('./Geometry/CutterExample'))],
   ['Geometry/TubeExample', lazy(() => import('./Geometry/TubeExample'))],
   // ['Volume/SliceRendering', lazy(() => import('./Volume/SliceRendering'))],
   // ['Volume/ImageSeriesRendering', lazy(() => import('./Volume/ImageSeriesRendering'))],

usage/src/Geometry/CutterExample.jsx

@@ -1,8 +1,10 @@
-import React from 'react';
-
 import { newInstance as newVtkPlaneInstance } from '@kitware/vtk.js/Common/DataModel/Plane.js';
 
-import { Algorithm, View, GeometryRepresentation, Reader } from 'react-vtk-js';
+// vtkCutter
+import '@kitware/vtk.js/Filters/Core/Cutter';
+// vtkOBJReader
+import '@kitware/vtk.js/IO/Misc/OBJReader';
+import { Algorithm, GeometryRepresentation, Reader, View } from 'react-vtk-js';
 
 function Example(props) {
   const plane = newVtkPlaneInstance({

usage/src/Geometry/OBJViewer.jsx

@@ -1,6 +1,6 @@
-import React from 'react';
-
-import { View, GeometryRepresentation, Reader } from 'react-vtk-js';
+// imports vtkOBJReader
+import '@kitware/vtk.js/IO/Misc/OBJReader';
+import { GeometryRepresentation, Reader, View } from 'react-vtk-js';
 
 // React complains about unique key prop but I don't see why
 function Example(props) {