add xml comments

src/Avalonia.Controls/Platform/ExtendClientAreaChromeHints.cs

@@ -2,13 +2,37 @@
 
 namespace Avalonia.Platform
 {
+    /// <summary>
+    /// Hint for Window Chrome when ClientArea is Extended.
+    /// </summary>
     [Flags]
     public enum ExtendClientAreaChromeHints
     {
+        /// <summary>
+        /// The will be no chrome at all.
+        /// </summary>
         NoChrome,
-        Default = SystemChrome,        
+
+        /// <summary>
+        /// The default for the platform.
+        /// </summary>
+        Default = SystemChrome,
+
+        /// <summary>
+        /// Use SystemChrome
+        /// </summary>
         SystemChrome = 0x01,
+
+        /// <summary>
+        /// Use system chrome where possible. OSX system chrome is used, Windows managed chrome is used.
+        /// This is because Windows Chrome can not be shown ontop of user content.
+        /// </summary>
         PreferSystemChrome = 0x02,
+
+        /// <summary>
+        /// On OSX the titlebar is the thicker toolbar kind. Causes traffic lights to be positioned
+        /// slightly lower than normal.
+        /// </summary>
         OSXThickTitleBar = 0x08,               
     }
 }