Change title of DocumentViewerWindow

Elwig/Windows/DocumentViewerWindow.xaml.cs

@@ -9,7 +9,7 @@ namespace Elwig.Windows {
 
         public DocumentViewerWindow(string title, string path) {
             InitializeComponent();
-            Title = Title + " - " + title;
+            Title = $"{title} - {Title}";
             WebView.Source = new($"file://{path}#view=FitH");
         }