Update PipeReader.xml to add info to AdvanceTo (#4311)

* Update PipeReader.xml to add info to AdvanceTo
Co-authored-by: Stephen Halter <[email protected]>

Author: Mathew-Kochekkan

xml/System.IO.Pipelines/PipeReader.xml

@@ -59,6 +59,7 @@
 
 The memory for the consumed data will be released and no longer available. The <xref:System.IO.Pipelines.ReadResult.Buffer%2A> previously returned from <xref:System.IO.Pipelines.PipeReader.ReadAsync(System.Threading.CancellationToken)> must not be accessed after this call. The examined data communicates to the pipeline when it should signal more data is available.
 
+
           ]]></format>
         </remarks>
       </Docs>
@@ -97,8 +98,11 @@ The memory for the consumed data will be released and no longer available.
 
 The <xref:System.IO.Pipelines.ReadResult.Buffer> previously returned from <xref:System.IO.Pipelines.PipeReader.ReadAsync(System.Threading.CancellationToken)> must not be accessed after this call.
 
+This is equivalent to calling <xref:System.IO.Pipelines.PipeReader.AdvanceTo(System.SequencePosition,System.SequencePosition)> with identical examined and consumed positions.
 The examined data communicates to the pipeline when it should signal more data is available.
 
+Because the consumed parameter doubles as the examined parameter, the consumed parameter should be greater than or equal to the examined position in the previous call to `AdvanceTo`. Otherwise, an <xref:System.InvalidOperationException> is thrown.
+
           ]]></format>
         </remarks>
       </Docs>
@@ -141,6 +145,8 @@ The <xref:System.IO.Pipelines.ReadResult.Buffer> previously returned from <xref:
 
 The examined data communicates to the pipeline when it should signal more data is available.
 
+The examined parameter should be greater than or equal to the examined position in the previous call to `AdvanceTo`. Otherwise, an <xref:System.InvalidOperationException> is thrown.
+
           ]]></format>
         </remarks>
       </Docs>