Fix line number settings migration (#41351)

Follow-up to https://github.com/zed-industries/zed/pull/39268

Also updates the documentation.

Release Notes:

- N/A

docs/src/configuring-zed.md

@@ -2996,11 +2996,33 @@ List of `string` glob patterns
 
 - Description: Whether to show relative line numbers in the gutter
 - Setting: `relative_line_numbers`
-- Default: `false`
+- Default: `"disabled"`
 
 **Options**
 
-`boolean` values
+1. Show relative line numbers in the gutter whilst counting wrapped lines as one line:
+
+```json [settings]
+{
+  "relative_line_numbers": "enabled"
+}
+```
+
+2. Show relative line numbers in the gutter, including wrapped lines in the counting:
+
+```json [settings]
+{
+  "relative_line_numbers": "wrapped"
+}
+```
+
+2. Do not use relative line numbers:
+
+```json [settings]
+{
+  "relative_line_numbers": "disabled"
+}
+```
 
 ## Remove Trailing Whitespace On Save