Update ArrayPool`1.xml (#4507)

* Update ArrayPool`1.xml
Co-authored-by: Stephen Toub <[email protected]>

Author: jkotas

xml/System.Buffers/ArrayPool`1.xml

@@ -199,7 +199,9 @@ The instance of the <xref:System.Buffers.ArrayPool%601> class created by this me
 ## Remarks  
 
 This buffer is loaned to the caller and should be returned to the same pool using the <xref:System.Buffers.ArrayPool%601.Return%2A> method, so that it can be reused in subsequent calls to the <xref:System.Buffers.ArrayPool%601.Rent%2A> method. Failure to return a rented buffer is not a fatal error. However, it may lead to decreased application performance, as the pool may need to create a new buffer to replace the lost one.
- ]]></format>
+
+The array returned by this method may not be zero-initialized. 
+]]></format>
         </remarks>
       </Docs>
     </Member>