Hi Eric,
The "notes" field can definitely be added in the project center views, such as the summary view. Then in Project Pro enter a comment/description on the project summary row (row 0) by double clicking on the row and navigating to the notes tab. After publishing, you'll see your comment in the notes column added to the project center view.
Note also that there are 3rd-party tools which allows bulk editing project custom fields in PWA in a view similar to the project center.
https://store.office.com/bulk-edit-WA104148561.aspx?assetid=WA104148561
https://help.fluentpro.com/fluentbooks_2013/wizards/bulk_edit/projects_bulk_edit/start