docs: add clipboard Fiddle examples (#20445)

* docs: add clipboard paste Fiddle example

* docs: add clipboard copy Fiddle example

* docs: add appropriate title to Fiddles

Co-Authored-By: John Kleinschmidt <jkleinsc@github.com>

docs/fiddles/system/clipboard/copy/renderer.js

@@ -0,0 +1,10 @@
+const { clipboard } = require('electron')
+
+const copyBtn = document.getElementById('copy-to')
+const copyInput = document.getElementById('copy-to-input')
+
+copyBtn.addEventListener('click', () => {
+  if (copyInput.value !== '') copyInput.value = ''
+  copyInput.placeholder = 'Copied! Paste here to see.'
+  clipboard.writeText('Electron Demo!')
+})