add swift-docc-plugin dep

Author: yngrtc

Package.swift

@@ -36,6 +36,7 @@ let package = Package(
         .library(name: "STUN", targets: ["STUN"]),
     ],
     dependencies: [
+        .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
         .package(url: "https://github.com/apple/swift-nio.git", from: "2.65.0"),
         .package(url: "https://github.com/apple/swift-crypto.git", from: "3.4.0"),
         .package(url: "https://github.com/swift-extras/swift-extras-base64.git", from: "1.0.0"),