Update tutorial-3-hooking-up-events.md

You’ll need to create your Global Object before loading content into your WebView that references the object.

All calls for creating the object and setting its properties should be made before calling WebView::LoadURL. WebView::CreateGlobalJavaScriptObject is a synchronous API call and is guaranteed to be completed once the method call returns.
Merge pull request #2 from trofian/patch-1

Update tutorial-3-hooking-up-events.md