Adds notes

src/Examine/LuceneEngine/Directories/SyncDirectory.cs

@@ -38,7 +38,7 @@ public class SyncDirectory : Lucene.Net.Store.Directory
         private bool _inSync = false;
         private readonly object _locker = new object();
 
-        private static readonly HashSet<string> RemoteOnly = new HashSet<string> {"segments.gen"};
+        internal static readonly HashSet<string> RemoteOnlyFiles = new HashSet<string> {"segments.gen"};
 
 
         /// <summary>
@@ -264,7 +264,7 @@ public override IndexInput OpenInput(string name)
             //generations approach. For example, the first segments file is segments_1, then segments_2, etc. 
             //The generation is a sequential long integer represented in alpha-numeric (base 36) form."
 
-            if (RemoteOnly.Contains(name))
+            if (RemoteOnlyFiles.Contains(name))
             {
                 return _masterDirectory.OpenInput(name);
             }

src/Examine/LuceneEngine/Directories/SyncIndexInput.cs

@@ -32,6 +32,10 @@ internal class SyncIndexInput : IndexInput
         /// </summary>
         /// <param name="directory"></param>
         /// <param name="name"></param>
+        /// <remarks>
+        /// This will not work for the segments.gen file because it doesn't compare to master and segments.gen is not write-once!
+        /// Therefore do not use this class from a Directory instance for that file, see SyncDirectory.OpenInput
+        /// </remarks>
         public SyncIndexInput(SyncDirectory directory, string name)
         {
             if (directory == null) throw new ArgumentNullException(nameof(directory));