sync: add some helpful comments

Notesnook.API/Controllers/AnnouncementController.cs

@@ -27,7 +27,7 @@ using Streetwriters.Data.Repositories;
 
 namespace Notesnook.API.Controllers
 {
-
+    // TODO: this should be moved out into its own microservice
     [ApiController]
     [Route("announcements")]
     public class AnnouncementController : ControllerBase

Notesnook.API/Hubs/SyncHub.cs

@@ -92,6 +92,9 @@ namespace Notesnook.API.Hubs
                 var data = transferItem.Items[i];
                 var type = transferItem.Types[i];
 
+                // We intentionally don't await here to speed up the sync. Fire and forget
+                // suits here because we don't really care if the item reaches the other
+                // devices.
                 others.SyncItem(
                         new SyncTransferItem
                         {