Update Selection of DataGrid.xml (#2814)

Thbe SelectionMode and SelectionUnit description incorrect

Author: xlgucytekbio

xml/System.Windows.Controls/DataGrid.xml

@@ -47,7 +47,7 @@
  You can use the <xref:System.Windows.Controls.DataGrid.Columns%2A> collection to programmatically add, insert, remove, and change any columns in the control at run time. Check the <xref:System.Windows.Controls.DataGridColumn.IsAutoGenerated%2A> property to determine whether a column is auto generated or user defined. Auto-generated columns will be automatically added, removed, or regenerated when the <xref:System.Windows.Controls.ItemsControl.ItemsSource%2A> changes.  
   
 ## Selection  
- By default, the entire row is selected when a user clicks a cell in a <xref:System.Windows.Controls.DataGrid>, and a user can select multiple rows. You can set the <xref:System.Windows.Controls.DataGrid.SelectionMode%2A> property to specify whether a user can select cells, full rows, or both. Set the <xref:System.Windows.Controls.DataGrid.SelectionUnit%2A> property to specify whether multiple rows or cells can be selected, or only single rows or cells.  
+ By default, the entire row is selected when a user clicks a cell in a <xref:System.Windows.Controls.DataGrid>, and a user can select multiple rows. You can set the <xref:System.Windows.Controls.DataGrid.SelectionUnit%2A> property to specify whether a user can select cells, full rows, or both. Set the <xref:System.Windows.Controls.DataGrid.SelectionMode%2A> property to specify whether multiple rows or cells can be selected, or only single rows or cells.  
   
  You can get information about the cells that are selected from the <xref:System.Windows.Controls.DataGrid.SelectedCells%2A> property. You can get information about cells for which selection has changed in the <xref:System.Windows.Controls.SelectedCellsChangedEventArgs> of the <xref:System.Windows.Controls.DataGrid.SelectedCellsChanged> event. Call the <xref:System.Windows.Controls.DataGrid.SelectAllCells%2A> or <xref:System.Windows.Controls.DataGrid.UnselectAllCells%2A> methods to programmatically select or unselect all cells. For more information, see [Default Keyboard and Mouse Behavior in the DataGrid Control](~/docs/framework/wpf/controls/default-keyboard-and-mouse-behavior-in-the-datagrid-control.md).  
   
@@ -5879,4 +5879,4 @@
       </Docs>
     </Member>
   </Members>
-</Type>
+</Type>