add "Note to Self"

Dear Christopher,

Not a problem, just a suggestion.

I have recently started using Rapid Contact Ex. I've used many other extensions, and I think you've produced a good one, with a very good user interface. I particularly like the Preview window that runs while I'm creating the fields.

Since that feature is so good, I suggest something similar, called "Note to Self". This would be a text area that would let me describe why I've done something in the field definition that I'm currently editing.

Scenario: 
On Day 1, I created a field called joining-household-number and made it a number.
On Day 2, I learnt about Field Groups, with dropdown values, but I was a bit confused.
On Day 3, I learnt more about Field Groups, and now I'd like to leave a note next to my new field that reminds me about the previous two days. I also want to explain to myself how the new field works.

Yes, I'd love to use the "Notes" field. But it's not visible in Joomla! 3x versions. Is it visible in J4?