docs: added windows -> create frameless window example (#20591)

* docs: added windows -> create frameless window example from electron-api-docs

* fixed style in accord with StandardJS

* removed class tag from button

docs/fiddles/windows/manage-windows/create-frameless-window/main.js

@@ -0,0 +1,25 @@
+const { app, BrowserWindow } = require('electron')
+
+let mainWindow = null
+
+function createWindow () {
+  const windowOptions = {
+    width: 600,
+    height: 400,
+    title: 'Create a frameless window',
+    webPreferences: {
+      nodeIntegration: true
+    }
+  }
+
+  mainWindow = new BrowserWindow(windowOptions)
+  mainWindow.loadFile('index.html')
+
+  mainWindow.on('closed', () => {
+    mainWindow = null
+  })
+}
+
+app.on('ready', () => {
+  createWindow()
+})