Show a description to the 'Quiet public' type of post

### Problem I have

I didn't know the functionality `Quiet public` until I saw today on a comment I was making.
I had to [search for it online](https://github.com/mastodon/mastodon/discussions/30425) in order to understand what it does.

### Solution I'd like

I'd like a description. I don't know what would be the best solution or even if there is already one implemented, but the first think I tried was just hovering the button:

### Alternatives considered

_No response_

### Other

If anyone has an interest idea on the UI/UX part, I might take the code to implement it.