docs: add example for taking screenshot (#20531)

docs/fiddles/media/screenshot/take-screenshot/main.js

@@ -0,0 +1,25 @@
+const { BrowserWindow, app } = require('electron')
+
+let mainWindow = null
+
+function createWindow () {
+  const windowOptions = {
+    width: 600,
+    height: 300,
+    title: 'Take a Screenshot',
+    webPreferences: {
+      nodeIntegration: true
+    }
+  }
+
+  mainWindow = new BrowserWindow(windowOptions)
+  mainWindow.loadFile('index.html')
+
+  mainWindow.on('closed', () => {
+    mainWindow = null
+  })
+}
+
+app.on('ready', () => {
+  createWindow()
+})