feat: add external notification tips

src/MaaWpfGui/Res/Localizations/zh-cn.xaml

@@ -22,6 +22,7 @@
     <system:String x:Key="AboutUs">关于我们</system:String>
     <system:String x:Key="Version">版本号</system:String>
     <system:String x:Key="Off">关闭</system:String>
+    <system:String x:Key="ExternalNotificationTips">请注意：外部通知功能目前仅会发送“所有任务完成”的通知。</system:String>
     <system:String x:Key="ExternalNotificationSettings">外部通知</system:String>
     <system:String x:Key="ExternalNotificationEnabled">启用的通知配置</system:String>
     <system:String x:Key="ExternalNotificationSendSuccess">发送成功</system:String>

src/MaaWpfGui/Views/UserControl/ExternalNotificationSettingsUserControl.xaml

@@ -26,12 +26,32 @@
             <RowDefinition />
             <RowDefinition />
             <RowDefinition />
+            <RowDefinition />
         </Grid.RowDefinitions>
 
         <StackPanel
             Grid.Row="0"
             Grid.Column="0"
             Orientation="Horizontal">
+            <Grid>
+                <Grid.ColumnDefinitions>
+                    <ColumnDefinition Width="65"/>
+                    <ColumnDefinition Width="420"/>
+                    <ColumnDefinition Width="65"/>
+                </Grid.ColumnDefinitions>
+            <controls:TextBlock
+                    Grid.Column="1"
+                    Margin="10"
+                    Block.TextAlignment="Center"
+                    Text="{DynamicResource ExternalNotificationTips}"
+                    TextWrapping="Wrap" />
+            </Grid>
+        </StackPanel>
+
+        <StackPanel
+            Grid.Row="1"
+            Grid.Column="0"
+            Orientation="Horizontal">
             <Grid>
                 <Grid.ColumnDefinitions>
                     <ColumnDefinition Width="35"/>
@@ -68,7 +88,7 @@
         </StackPanel>
 
         <StackPanel
-            Grid.Row="1"
+            Grid.Row="2"
             Grid.Column="0"
             IsEnabled="{c:Binding IsServerChan}"
             Orientation="Horizontal">
@@ -98,7 +118,7 @@
         </StackPanel>
 
         <StackPanel
-            Grid.Row="2"
+            Grid.Row="3"
             Grid.Column="0"
             IsEnabled="{c:Binding IsSmtp}"
             Orientation="Horizontal">