Add swift-docc-plugin and example theme-settings.json to swift-argument-parser

add-plugin-and-settings.diff

diff --git a/[email protected] b/[email protected]
index b70ee3a..228bd37 100644
--- a/[email protected]
+++ b/[email protected]
@@ -22,7 +22,9 @@ var package = Package(
             name: "GenerateManual",
             targets: ["GenerateManual"]),
     ],
-    dependencies: [],
+    dependencies: [
+      .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.1.0"),
+    ],
     targets: [
         // Core Library
         .target(
diff --git a/Sources/ArgumentParser/Documentation.docc/theme-settings.json b/Sources/ArgumentParser/Documentation.docc/theme-settings.json
new file mode 100644
index 0000000..2222f1d
--- /dev/null
+++ b/Sources/ArgumentParser/Documentation.docc/theme-settings.json
@@ -0,0 +1,9 @@
+{
+  "features": {
+    "docs": {
+      "quickNavigationPreview": {
+        "enable": true
+      }
+    }
+  }
+}