menu: add devtools accelerator for darwin

Author: evanlucas

lib/menus/darwin.js

@@ -24,7 +24,10 @@ module.exports = [
   }
 , { label: 'View'
   , submenu: [
-      { label: 'Toggle DevTools', command: 'application:devtools' }
+      { label: 'Toggle DevTools'
+      , accelerator: 'CmdOrCtrl+Alt+I'
+      , command: 'application:devtools'
+      }
     , { type: 'separator' }
     , { label: 'Next Panel'
       , accelerator: 'CommandOrControl+Alt+Down'