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/editor/src/editor_settings.rs

@@ -14,11 +14,15 @@ pub struct EditorSettings {
     pub seed_search_query_from_cursor: SeedQuerySetting,
 }
 
+/// When to populate a new search's query based on the text under the cursor.
 #[derive(Copy, Clone, Debug, Serialize, Deserialize, PartialEq, Eq, JsonSchema)]
 #[serde(rename_all = "snake_case")]
 pub enum SeedQuerySetting {
+    /// Always populate the search query with the word under the cursor.
     Always,
+    /// Only populate the search query when there is text selected.
     Selection,
+    /// Never populate the search query
     Never,
 }
 
@@ -29,31 +33,75 @@ pub struct Scrollbar {
     pub selections: bool,
 }
 
+/// When to show the scrollbar in the editor.
+///
+/// Default: auto
 #[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
 #[serde(rename_all = "snake_case")]
 pub enum ShowScrollbar {
+    /// Show the scrollbar if there's important information or
+    /// follow the system's configured behavior.
     Auto,
+    /// Match the system's configured behavior.
     System,
+    /// Always show the scrollbar.
     Always,
+    /// Never show the scrollbar.
     Never,
 }
 
 #[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
 pub struct EditorSettingsContent {
+    /// Whether the cursor blinks in the editor.
+    ///
+    /// Default: true
     pub cursor_blink: Option<bool>,
+    /// Whether to show the informational hover box when moving the mouse
+    /// over symbols in the editor.
+    ///
+    /// Default: true
     pub hover_popover_enabled: Option<bool>,
+    /// Whether to pop the completions menu while typing in an editor without
+    /// explicitly requesting it.
+    ///
+    /// Default: true
     pub show_completions_on_input: Option<bool>,
+    /// Whether to display inline and alongside documentation for items in the
+    /// completions menu.
+    ///
+    /// Default: true
     pub show_completion_documentation: Option<bool>,
+    /// Whether to use additional LSP queries to format (and amend) the code after
+    /// every "trigger" symbol input, defined by LSP server capabilities.
+    ///
+    /// Default: true
     pub use_on_type_format: Option<bool>,
+    /// Scrollbar related settings
     pub scrollbar: Option<ScrollbarContent>,
+    /// Whether the line numbers on editors gutter are relative or not.
+    ///
+    /// Default: false
     pub relative_line_numbers: Option<bool>,
+    /// When to populate a new search's query based on the text under the cursor.
+    ///
+    /// Default: always
     pub seed_search_query_from_cursor: Option<SeedQuerySetting>,
 }
 
+/// Scrollbar related settings
 #[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
 pub struct ScrollbarContent {
+    /// When to show the scrollbar in the editor.
+    ///
+    /// Default: auto
     pub show: Option<ShowScrollbar>,
+    /// Whether to show git diff indicators in the scrollbar.
+    ///
+    /// Default: true
     pub git_diff: Option<bool>,
+    /// Whether to show buffer search result markers in the scrollbar.
+    ///
+    /// Default: true
     pub selections: Option<bool>,
 }