Document System.Runtime.InteropServices.Swift namespace (#10227)

Author: jkoritzinsky

xml/ns-System.Runtime.InteropServices.Swift.xml

@@ -1,6 +1,6 @@
 <Namespace Name="System.Runtime.InteropServices.Swift">
   <Docs>
-    <summary>To be added.</summary>
-    <remarks>To be added.</remarks>
+    <summary>Support types for .NET interop with Swift code.</summary>
+    <remarks>These types are used by low level interop and code-generation tools to enable interop between .NET code and Swift code.</remarks>
   </Docs>
 </Namespace>