Update docs for Swift debugging (#33483)

Release Notes:

- N/A *or* Added/Fixed/Improved ...

docs/src/languages/swift.md

@@ -5,7 +5,34 @@ Report issues to: [https://github.com/zed-extensions/swift/issues](https://githu
 
 - Tree-sitter: [alex-pinkus/tree-sitter-swift](https://github.com/alex-pinkus/tree-sitter-swift)
 - Language Server: [swiftlang/sourcekit-lsp](https://github.com/swiftlang/sourcekit-lsp)
+- Debug Adapter: [`lldb-dap`](https://github.com/swiftlang/llvm-project/blob/next/lldb/tools/lldb-dap/README.md)
 
-## Configuration
+## Language Server Configuration
 
 You can modify the behavior of SourceKit LSP by creating a `.sourcekit-lsp/config.json` under your home directory or in your project root. See [SourceKit-LSP configuration file](https://github.com/swiftlang/sourcekit-lsp/blob/main/Documentation/Configuration%20File.md) for complete documentation.
+
+## Debugging
+
+The Swift extension provides a debug adapter for debugging Swift code.
+Zed's name for the adapter (in the UI and `debug.json`) is `Swift`, and under the hood it uses [`lldb-dap`](https://github.com/swiftlang/llvm-project/blob/next/lldb/tools/lldb-dap/README.md), as provided by the Swift toolchain.
+The extension tries to find an `lldb-dap` binary using `swiftly`, using `xcrun`, and by searching `$PATH`, in that order of preference.
+The extension doesn't attempt to download `lldb-dap` if it's not found.
+
+### Examples
+
+#### Build and debug a Swift binary
+
+```json
+[
+  {
+    "label": "Debug Swift",
+    "build": {
+      "command": "swift",
+      "args": ["build"]
+    },
+    "program": "$ZED_WORKTREE_ROOT/swift-app/.build/arm64-apple-macosx/debug/swift-app",
+    "request": "launch",
+    "adapter": "Swift"
+  }
+]
+```