update summary for ConfigurationBinder.GetValue<T> to clarify default return

Author: MashalMohammed

xml/Microsoft.Extensions.Configuration/ConfigurationBinder.xml

@@ -651,8 +651,8 @@ For more information and examples, see [Binding](/dotnet/core/extensions/configu
         <typeparam name="T">The type to convert the value to.</typeparam>
         <param name="configuration">The configuration.</param>
         <param name="key">The key of the configuration section's value to convert.</param>
-        <summary>Extracts the value with the specified key and converts it to type T.</summary>
-        <returns>The converted value.</returns>
+        <summary>Extracts the value with the specified key and converts it to type T. Returns default if the key is not present.</summary>
+        <returns>The converted value or the default.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>