Fix incorrect app icon asset

Multiplatform/Shared/Assets.xcassets/AppIcon.appiconset/Contents.json

@@ -139,7 +139,7 @@
       "size" : "128x128"
     },
     {
-      "filename" : "icon_256x256@2x.png",
+      "filename" : "icon_128x128@2x.png",
       "idiom" : "mac",
       "scale" : "2x",
       "size" : "128x128"

Multiplatform/Shared/SwiftUIView.swift

@@ -0,0 +1,21 @@
+//
+//  SwiftUIView.swift
+//  NetNewsWire
+//
+//  Created by Maurice Parker on 6/28/20.
+//  Copyright © 2020 Ranchero Software. All rights reserved.
+//
+
+import SwiftUI
+
+struct SwiftUIView: View {
+    var body: some View {
+        Text(/*@START_MENU_TOKEN@*/"Hello, World!"/*@END_MENU_TOKEN@*/)
+    }
+}
+
+struct SwiftUIView_Previews: PreviewProvider {
+    static var previews: some View {
+        SwiftUIView()
+    }
+}