Document System.Collections.Generic.IEnumerable<TSource> (#3671)

* Document System.Collections.Generic.IEnumerable<TSource>

* suggestions by gewarren

Co-Authored-By: Genevieve Warren <[email protected]>

Author: carlossanlop

xml/System.Linq/Enumerable.xml

@@ -9567,12 +9567,22 @@ Only unique elements are returned.
         <Parameter Name="count" Type="System.Int32" Index="1" FrameworkAlternate="netcore-2.0;netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1;netcore-3.1" />
       </Parameters>
       <Docs>
-        <typeparam name="TSource">To be added.</typeparam>
-        <param name="source">To be added.</param>
-        <param name="count">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <typeparam name="TSource">The type of the elements in the enumerable collection.</typeparam>
+        <param name="source">An enumerable collection instance.</param>
+        <param name="count">The number of elements to omit from the end of the collection.</param>
+        <summary>Returns a new enumerable collection that contains the elements from <paramref name="source" /> with the last <paramref name="count" /> elements of the source collection omitted.</summary>
+        <returns>A new enumerable collection that contains the elements from <paramref name="source" /> minus <paramref name="count" /> elements from the end of the collection.</returns>
+        <remarks>
+          <format type="text/markdown"><![CDATA[
+
+## Remarks
+
+If `count` is not a positive number, this method returns an identical copy of the `source` enumerable collection.
+
+          ]]></format>
+        </remarks>
+        <exception cref="T:System.ArgumentNullException">
+          <paramref name="source" /> is <see langword="null" />.</exception>
       </Docs>
     </Member>
     <MemberGroup MemberName="SkipWhile&lt;TSource&gt;">
@@ -11193,12 +11203,22 @@ Only unique elements are returned.
         <Parameter Name="count" Type="System.Int32" Index="1" FrameworkAlternate="netcore-2.0;netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1;netcore-3.1" />
       </Parameters>
       <Docs>
-        <typeparam name="TSource">To be added.</typeparam>
-        <param name="source">To be added.</param>
-        <param name="count">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <typeparam name="TSource">The type of the elements in the enumerable collection.</typeparam>
+        <param name="source">An enumerable collection instance.</param>
+        <param name="count">The number of elements to take from the end of the collection.</param>
+        <summary>Returns a new enumerable collection that contains the last <paramref name="count" /> elements from <paramref name="source" />.</summary>
+        <returns>A new enumerable collection that contains the last <paramref name="count" /> elements from <paramref name="source" />.</returns>
+        <remarks>
+          <format type="text/markdown"><![CDATA[
+
+## Remarks
+
+If `count` is not a positive number, this method returns an empty enumerable collection.
+
+          ]]></format>
+        </remarks>
+        <exception cref="T:System.ArgumentNullException">
+          <paramref name="source" /> is <see langword="null" />.</exception>
       </Docs>
     </Member>
     <MemberGroup MemberName="TakeWhile&lt;TSource&gt;">