Document namespace System.Threading.Tasks.Sources (#3231)

Author: carlossanlop

xml/ns-System.Threading.Tasks.Sources.xml

@@ -1,6 +1,6 @@
 <Namespace Name="System.Threading.Tasks.Sources">
   <Docs>
-    <summary>To be added.</summary>
+    <summary>Provides types for creating <see cref="T:System.Threading.Tasks.ValueTask" /> and <see cref="T:System.Threading.Tasks.ValueTask`1" /> optimized to minimize allocations. The <see cref="T:System.Threading.Tasks.Sources.IValueTaskSource" /> and <see cref="T:System.Threading.Tasks.Sources.IValueTaskSource`1" /> interfaces can be implemented on objects used to provide the backing implementations for <see cref="T:System.Threading.Tasks.ValueTask" /> and <see cref="T:System.Threading.Tasks.ValueTask`1" />, and <see cref="T:System.Threading.Tasks.Sources.ManualResetValueTaskSourceCore`1" /> can be used to implement the core logic necessary to support the task lifecycle. These are advanced types and need only be used in specialized situations where performance is paramount.</summary>
     <remarks>To be added.</remarks>
   </Docs>
 </Namespace>