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/welcome/src/base_keymap_setting.rs

@@ -4,6 +4,9 @@ use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use settings::Settings;
 
+/// Base key bindings scheme. Base keymaps can be overriden with user keymaps.
+///
+/// Default: VSCode
 #[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq, Default)]
 pub enum BaseKeymap {
     #[default]