Add hint text or placeholder to suggest that this section is editable

Right now when you expand a card in the Kanban board/ Grid/ Calendar you get the UI shown in the screenshot. It would be nice if there was some hint text that suggested to the user that you can edit this section marked with red.

How to Reproduce

  1. Open AppFlowy
  2. Create a new Kanban/Grid/Calendar
  3. Create and open a new card
  4. Observe that there is no visual clue to suggest the user that this area is editable.

Expected Behavior

Some visual clue to show that this area is editable.