update<Hotkeys>: add STAGE/UNSTAGE hotkey description

src/Resources/Locales/en_US.xaml

@@ -464,6 +464,7 @@
     <sys:String x:Key="Text.Hotkeys.SwitchTo">Switch to page at given index</sys:String>
     <sys:String x:Key="Text.Hotkeys.Search">Toggle search bar if possible</sys:String>
     <sys:String x:Key="Text.Hotkeys.Refresh">Reload current repository if possible</sys:String>
+    <sys:String x:Key="Text.Hotkeys.ToggleStage">Stage or unstage selected files</sys:String>
 
     <sys:String x:Key="Text.NotConfigured">Git has NOT been configured. Please to go [Preference] and configure it first.</sys:String>
     <sys:String x:Key="Text.PathNotFound">Path[{0}] not exists!</sys:String>

src/Resources/Locales/zh_CN.xaml

@@ -463,6 +463,7 @@
     <sys:String x:Key="Text.Hotkeys.SwitchTo">切换到指定位置的标签页</sys:String>
     <sys:String x:Key="Text.Hotkeys.Search">打开/隐藏搜索框（仅在仓库页起效）</sys:String>
     <sys:String x:Key="Text.Hotkeys.Refresh">重新加载当前仓库信息（仅在仓库页起效）</sys:String>
+    <sys:String x:Key="Text.Hotkeys.ToggleStage">暂存或从暂存中移除当前选中</sys:String>
 
     <sys:String x:Key="Text.NotConfigured">GIT尚未配置。请打开【偏好设置】配置GIT路径。</sys:String>
     <sys:String x:Key="Text.PathNotFound">路径（{0}）不存在或不可读取!</sys:String>

src/Views/Hotkeys.xaml.cs

@@ -24,6 +24,7 @@ namespace SourceGit.Views {
                 new Keymap("CTRL + [1-9]", "SwitchTo"),
                 new Keymap("CTRL + F", "Search"),
                 new Keymap("F5", "Refresh"),
+                new Keymap("SPACE", "ToggleStage"),
             };
         }