Updates XML documentation to call out prereq of LoadShedding. (#5387)

- Must have a registered implementation of `IHostEnvironmentStatistics` for `LoadShedding` to function.

src/Orleans.Core/Configuration/Options/LoadSheddingOptions.cs

@@ -1,11 +1,16 @@
 
+using Orleans.Statistics;
+
 namespace Orleans.Configuration
 {
     public class LoadSheddingOptions
     {
         /// <summary>
         /// Specifies whether or not load shedding in the client gateway and stream providers is enabled.
         /// The default value is false, meaning that load shedding is disabled.
+        ///
+        /// In addition to LoadSheddingEnabled being true, in order for the cluster to utilize LoadShedding
+        /// a valid <see cref="IHostEnvironmentStatistics"/> implementation must be registered within the ISiloHost.
         /// </summary>
         public bool LoadSheddingEnabled { get; set; }