Improve documentation for IFindFluent.Limit to note behaviour when passing zero or null (#804)

Author: leandromoh

Diff for: src/MongoDB.Driver/IFindFluent.cs

@@ -112,6 +112,9 @@ public interface IFindFluent<TDocument, TProjection> : IAsyncCursorSource<TProje
         /// <summary>
         /// Limits the number of documents.
         /// </summary>
+        /// <remarks>
+        /// Limit of zero or null is equivalent to setting no limit.
+        /// </remarks>
         /// <param name="limit">The limit.</param>
         /// <returns>The fluent find interface.</returns>
         IFindFluent<TDocument, TProjection> Limit(int? limit);