added missing param (#3802)

* added missing param

* Update type argument descriptions

Co-authored-by: Genevieve Warren <[email protected]>

Author: mairaw

xml/Microsoft.VisualC.StlClr/BinaryDelegate`3.xml

@@ -36,12 +36,12 @@
     <ReturnType>TResult</ReturnType>
   </ReturnValue>
   <Docs>
-    <typeparam name="TArg1">The first delegate argument.</typeparam>
-    <typeparam name="TArg2">The second delegate argument.</typeparam>
+    <typeparam name="TArg1">The type of the first delegate argument.</typeparam>
+    <typeparam name="TArg2">The type of the second delegate argument.</typeparam>
     <typeparam name="TResult">The return type of the delegate.</typeparam>
     <param name="A_0">The first argument.</param>
     <param name="">The first argument.</param>
-    <param name="">To be added.</param>
+    <param name="">The second argument.</param>
     <param name="A_1">The second argument.</param>
     <summary>Describes a two-argument delegate. You use it to specify the arguments and return type of the delegate.</summary>
     <returns>The return type of the delegate.</returns>