docs: add exemplary fiddle for `launch in fiddle` feat (#19785)

* add fit-screen

* new url format

* nit

docs/api/screen.md

@@ -14,7 +14,7 @@ property, so writing `let { screen } = require('electron')` will not work.
 
 An example of creating a window that fills the whole screen:
 
-```javascript
+```javascript fiddle='docs/fiddles/screen/fit-screen'
 const { app, BrowserWindow, screen } = require('electron')
 
 let win

docs/fiddles/screen/fit-screen/main.js

@@ -0,0 +1,20 @@
+// Retrieve information about screen size, displays, cursor position, etc.
+//
+// For more info, see:
+// https://electronjs.org/docs/api/screen
+
+const { app, BrowserWindow } = require('electron')
+
+let mainWindow = null
+
+app.on('ready', () => {
+  // We cannot require the screen module until the app is ready.
+  const { screen } = require('electron')
+
+  // Create a window that fills the screen's available work area.
+  const primaryDisplay = screen.getPrimaryDisplay()
+  const { width, height } = primaryDisplay.workAreaSize
+
+  mainWindow = new BrowserWindow({ width, height })
+  mainWindow.loadURL('https://electronjs.org')
+})