Link to System.Text.Json overview (#3307)

Author: tdykstra

xml/ns-System.Text.Json.xml

@@ -1,6 +1,12 @@
 <Namespace Name="System.Text.Json">
   <Docs>
     <summary>The System.Text.Json namespace provides high-performance, low-allocating, and standards-compliant capabilities to process JavaScript Object Notation (JSON), which includes serializing objects to JSON text and deserializing JSON text to objects, with UTF-8 support built-in. It also provides types to read and write JSON text encoded as UTF-8, and to create an in-memory document object model (DOM) for random access of the JSON elements within a structured view of the data.</summary>
-    <remarks>To be added.</remarks>
+    <remarks>
+          <format type="text/markdown"><![CDATA[
+## Remarks
+
+For more information, see the [System.Text.Json overview](/dotnet/standard/serialization/system-text-json-overview).
+          ]]></format>
+      </remarks>
   </Docs>
 </Namespace>