HttpContent: Buffering is implementation dependent (#10108)

Author: breyed

xml/System.Net.Http/HttpContent.xml

@@ -879,6 +879,7 @@ When the `disposing` parameter is `true`, this method releases all resources hel
 ## Remarks
 
  Note that this method will internally buffer the content unless <xref:System.Net.Http.HttpContent.CreateContentReadStream(System.Threading.CancellationToken)> has been implemented to do otherwise.
+ For example, when using <xref:System.Net.Http.HttpClient>, a method such as <xref:System.Net.Http.HttpClient.SendAsync%2A> returns a class derived from <xref:System.Net.Http.HttpContent> that conditionally buffers based on what's passed for the `completionOption` parameter.
 
  ]]></format>
         </remarks>
@@ -1047,7 +1048,8 @@ When the `disposing` parameter is `true`, this method releases all resources hel
           <format type="text/markdown"><![CDATA[
 
 ## Remarks
- This operation will not block. The returned <xref:System.Threading.Tasks.Task%601> object will complete after all of the stream that represents content has been read.
+ This operation will not block. The returned <xref:System.Threading.Tasks.Task%601> object will complete after all of the stream that represents content has been read (unless <xref:System.Net.Http.HttpContent.CreateContentReadStream(System.Threading.CancellationToken)> has been implemented to do otherwise).
+For example, when using <xref:System.Net.Http.HttpClient>, a method such as <xref:System.Net.Http.HttpClient.SendAsync%2A> returns a class derived from <xref:System.Net.Http.HttpContent> that conditionally buffers based on what's passed for the `completionOption` parameter.
 
  Once the operation completes, the <xref:System.Threading.Tasks.Task%601.Result%2A> property on the returned task object contains the stream that represents the HTTP content. The returned stream can then be used to read the content using various stream APIs.