Where can I add notes

I am searching for a way to add personnal notes in a app building. Reason is when I am building an app I know what I am doing, but afterwards sometimes I am trying to understand what I did. A simple note page available from the settings page would be perfect.

If you click on the name of your app in the editor pane at the top left you will see this capability:


thanks @ScottR sorry I missed that part.