Improve summary for DecimalPlaces (#3480)

* Improve summary for DecimalPlaces

* fix cref syntax

Author: mairaw

xml/System.Windows.Forms/NumericUpDown.xml

@@ -229,7 +229,7 @@
         <ReturnType>System.Int32</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>Gets or sets the number of decimal places to display in the spin box (also known as an up-down control).</summary>
+        <summary>Gets or sets the number of decimal places to display in the spin box (also known as an up-down control). This property doesn't affect the <see cref="P:System.Windows.Forms.NumericUpDown.Value" /> property.</summary>
         <value>The number of decimal places to display in the spin box. The default is 0.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[