add(widget/Spacer): empty widget implementation

src/main.zig

@@ -34,15 +34,18 @@ pub fn main() !void {
     var appFileText = App.Widget.RawText.init(allocator, appFile);
     appFile.close();
 
+    var spacer = App.Widget.Spacer.init();
     var framing = App.Layout.Framing.init(allocator, .{
         .widget = App.Widget.createFrom(&mainFileText),
     });
     var hstack = App.Layout.HStack.init(allocator, .{
         App.Layout.createFrom(&framing),
     });
+    // TODO: corresponding contents need to be filled out by the layout accordingly!
     var vstack = App.Layout.VStack.init(allocator, .{
         App.Widget.createFrom(&appFileText),
         App.Layout.createFrom(&hstack),
+        App.Widget.createFrom(&spacer),
     });
     var layout = App.Layout.createFrom(&vstack);
     defer layout.deinit();