Document System.IO.Enumeration.FileSystemEnumerator (#3412)

* Document System.IO.Enumeration.FileSystemEnumerator.TransformEntry

* Finish documenting the rest of the APIs in this file

* remove extra >

Author: carlossanlop

xml/System.IO.Enumeration/FileSystemEnumerator`1.xml

@@ -31,8 +31,8 @@
     </Interface>
   </Interfaces>
   <Docs>
-    <typeparam name="TResult">To be added.</typeparam>
-    <summary>To be added.</summary>
+    <typeparam name="TResult">The type of the result produced by this file system enumerator.</typeparam>
+    <summary>Enumerates the file system elements of the provided type that are being searched and filtered by a <see cref="T:System.IO.Enumeration.FileSystemEnumerable`1" />.</summary>
     <remarks>To be added.</remarks>
   </Docs>
   <Members>
@@ -382,7 +382,7 @@ As described in the remarks for <xref:System.Collections.IEnumerator>, the `Rese
         <Parameter Name="entry" Type="System.IO.Enumeration.FileSystemEntry" RefType="ref" />
       </Parameters>
       <Docs>
-        <param name="entry">To be added.</param>
+        <param name="entry">A file system entry reference.</param>
         <summary>When overridden in a derived class, generates the result type from the current entry.</summary>
         <returns>The result type from the current entry.</returns>
         <remarks>To be added.</remarks>