Add macOS specific speaking roles for MenuItem

docs/api/menu.md

@@ -133,6 +133,23 @@ if (process.platform === 'darwin') {
       }
     ]
   })
+  // Edit menu.
+  template[1].submenu.push(
+    {
+      type: 'separator'
+    },
+    {
+      label: 'Speech',
+      submenu: [
+        {
+          role: 'startspeaking'
+        },
+        {
+          role: 'stopspeaking'
+        }
+      ]
+    }
+  )
   // Window menu.
   template[3].submenu = [
     {