Adds notes

src/Umbraco.Core/Sync/DatabaseServerRegistrar.cs

@@ -7,6 +7,10 @@ namespace Umbraco.Core.Sync
     /// <summary>
     /// A registrar that stores registered server nodes in the database.
     /// </summary>
+    /// <remarks>
+    /// This is the default registrar which determines a server's role by using a master election process.
+    /// The master election process doesn't occur until just after startup so this election process doesn't really affect the primary startup phase.
+    /// </remarks>
     public sealed class DatabaseServerRegistrar : IServerRegistrar
     {
         private readonly Lazy<IServerRegistrationService> _registrationService;

src/Umbraco.Core/Sync/SingleServerRegistrar.cs

@@ -3,6 +3,14 @@ using System.Collections.Generic;
 
 namespace Umbraco.Core.Sync
 {
+    /// <summary>
+    /// Can be used when Umbraco is definitely not operating in a Load Balanced scenario to micro-optimize some startup performance
+    /// </summary>
+    /// <remarks>
+    /// The micro optimization is specifically to avoid a DB query just after the app starts up to determine the <see cref="ServerRole"/>
+    /// which by default is done with master election by a database query. The master election process doesn't occur until just after startup
+    /// so this micro optimization doesn't really affect the primary startup phase.
+    /// </remarks>
     public class SingleServerRegistrar : IServerRegistrar
     {
         private readonly IRuntimeState _runtime;
@@ -13,7 +21,7 @@ namespace Umbraco.Core.Sync
         public SingleServerRegistrar(IRuntimeState runtime)
         {
             _runtime = runtime;
-            _registrations = new Lazy<IServerAddress[]>(() => new[] { new ServerAddressImpl(_runtime.ApplicationUrl.ToString()) });
+            _registrations = new Lazy<IServerAddress[]>(() => new IServerAddress[] { new ServerAddressImpl(_runtime.ApplicationUrl.ToString()) });
         }
 
         public ServerRole GetCurrentServerRole()