Make sure you're working in Salesforce Classic to access Field Sets
To add a column, such as Description, to the Where-Used tab:
1. Setup, Create, Objects
2. Open the object Assembly (or Where Used for Spring '18/earlier versions)
3. Go to Field Sets
4. Edit the Field Sets Where Used Immediate/Top (pre-Summer '18: Default Where Used)
5. Select field set (i.e. Parent Item (Revision))
6. Drag your desired field down into the Field Set.
7. Save your changes.
8. Go to Propel Setup and Refresh Page Layouts.
Your new field will now appear on the Where-Used tab.