add swift-docc-plugin, Package.resolved

Author: lukepistrol

Package.resolved

@@ -13,6 +13,7 @@ let package = Package(
             targets: ["CodeEditKit"]),
     ],
     dependencies: [
+        .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
         // Dependencies declare other packages that this package depends on.
         // .package(url: /* package url */, from: "1.0.0"),
     ],