C#: Add missing QL doc

csharp/ql/src/semmle/code/csharp/security/dataflow/flowsinks/Email.qll

@@ -4,6 +4,7 @@ import csharp
 private import Remote
 private import semmle.code.csharp.frameworks.system.net.Mail
 
+/** Provides sinks for emails. */
 module Email {
   /** A data flow sink for sending email. */
   abstract class Sink extends DataFlow::ExprNode, RemoteFlowSink { }

csharp/ql/src/semmle/code/csharp/security/dataflow/flowsinks/Html.qll

@@ -172,6 +172,7 @@ class WebPageWriteLiteralToSink extends HtmlSink {
   }
 }
 
+/** An ASP.NET Core HTML sink. */
 abstract class AspNetCoreHtmlSink extends HtmlSink { }
 
 /**