Document Json namespaces (#2906)

* Document Json namespaces

* suggestions by rpetrusha

Co-Authored-By: Ron Petrusha <[email protected]>

* suggestion by ahsonkhan

Co-Authored-By: Ahson Khan <[email protected]>

Author: 2 people

xml/ns-System.Text.Json.Serialization.xml

@@ -1,6 +1,6 @@
 <Namespace Name="System.Text.Json.Serialization">
   <Docs>
-    <summary>To be added.</summary>
+    <summary>The System.Text.Json.Serialization namespace contains classes that are used to customize and extend serialization and deserialization of objects into JSON formatted documents or streams, either via an attribute model or via type converters.</summary>
     <remarks>To be added.</remarks>
   </Docs>
 </Namespace>

xml/ns-System.Text.Json.xml

@@ -1,6 +1,6 @@
 <Namespace Name="System.Text.Json">
   <Docs>
-    <summary>To be added.</summary>
+    <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>
   </Docs>
 </Namespace>