Display setting documentation in settings.json (#3936)

Let this screenshot of settings.json speak for itself: 

![image](https://github.com/zed-industries/zed/assets/24362066/fca60383-1788-43f9-803b-00f083394c8a)

Release Notes:
- Added code completion & on-hover documentation to Zed's settings.json
file.

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/vim/src/vim.rs

@@ -33,6 +33,9 @@ use workspace::{self, Workspace};
 
 use crate::state::ReplayableAction;
 
+/// Whether or not to enable Vim mode (work in progress).
+///
+/// Default: false
 pub struct VimModeSetting(pub bool);
 
 #[derive(Clone, Deserialize, PartialEq)]