Make sure horizontally size good

Author: Jack251970

Flow.Launcher/ReleaseNotesWindow.xaml

@@ -171,9 +171,9 @@
                     Grid.Row="2"
                     Grid.Column="0"
                     Grid.ColumnSpan="5"
+                    Width="500"
                     Height="500"
                     Margin="15 0 20 0"
-                    HorizontalAlignment="Stretch"
                     ClickAction="SafetyDisplayWithRelativePath"
                     Loaded="MarkdownViewer_Loaded"
                     Plugins="{StaticResource MdXamlPlugins}"