Add xml comment to ListExtensions.IndexOf method

Author: AlexUstinov

Orm/Xtensive.Orm/Core/Extensions/ListExtensions.cs

@@ -17,6 +17,14 @@ namespace Xtensive.Core
   /// </summary>
   public static class ListExtensions
   {
+    /// <summary>
+    /// Searches for the specified <paramref name="item"/> and returns the zero-based index
+    /// of the first occurence within the entire <paramref name="list"/>.
+    /// </summary>
+    /// <param name="list">An instance implementing <see cref="IReadOnlyList{T}"/> to be searched.</param>
+    /// <param name="item">An item to be looked for.</param>
+    /// <returns>A zero based index of the specified <paramref name="item"/> if found;
+    /// otherwise <c>-1</c>.</returns>
     public static int IndexOf<T>(this IReadOnlyList<T> list, T item)
     {
       var comparer = EqualityComparer<T>.Default;