Update CODEOWNERS - add extra people (#3905)

From experience with the 2.0 and 3.0 efforts, the people added in these PRs as additional area owners, were actively involved in the process of either writing the documentation or helping delegate the work.

Author: carlossanlop

.github/CODEOWNERS

@@ -25,11 +25,12 @@
 /xml/System.ComponentModel**/** @JeremyKuhne @safern
 /xml/System.ComponentModel.Composition**/** @maryamariyan @ViktorHofer
 /xml/System.ComponentModel.DataAnnotations**/** @lajones @ajcvickers
+/xml/System.ComponentModel.Design**/** @RussKie @merriemcgaw
 /xml/System.Composition**/** @maryamariyan @ViktorHofer
 /xml/System.Configuration**/** @maryamariyan @safern
 /xml/System.Data**/** @ajcvickers @cheenamalhotra @david-engel
 /xml/System.Data.SqlClient**/** @cheenamalhotra @david-engel @karinazhou @JRahnama
-/xml/System.Diagnostics**/** @tommcdon @krwq
+/xml/System.Diagnostics**/** @tommcdon @sywhang @krwq
 /xml/System.Diagnostics/DiagnosticSource.xml @Anipik
 /xml/System.Diagnostics/EventLog*.xml @Anipik
 /xml/System.Diagnostics/PerformanceCounter*.xml @Anipik
@@ -72,7 +73,7 @@
 /xml/System.Transactions**/** @dasetser @HongGit
 /xml/System.Web**/** @scottaddie
 /xml/System.Windows**/** @vatsan-madhavan
-/xml/System.Windows.Forms**/** @RussKie
+/xml/System.Windows.Forms**/** @RussKie @merriemcgaw
 /xml/System.Xaml**/** @vatsan-madhavan
 /xml/System.Xml**/** @buyaa-n @krwq