Fixing deceptive description of InitialOffsetProvider (#224)

src/Microsoft.Azure.EventHubs.Processor/EventProcessorOptions.cs

@@ -79,10 +79,10 @@ public bool EnableReceiverRuntimeMetric
         public int PrefetchCount { get; set; }
 
         /// <summary>
-        /// Get or sets the current function used to determine the initial offset at which to start receiving
-        /// events for a partition.
-        /// <para>A null return indicates that it is using the internal provider, which uses the last checkpointed
-        /// offset value (if present) or StartOfSTream (if not).</para>
+        /// Gets or sets a delegate which is used to get the initial offset for a given partition to create <see cref="PartitionReceiver"/>.
+        /// Delegate is invoked by passing in PartitionId and then user can return either the starting offset as string or starting UTC time
+        /// for receiving messages.
+        /// This is only used when <see cref="Lease.Offset"/> is not provided and receiver is being created for the very first time.
         /// </summary>
         public Func<string, object> InitialOffsetProvider { get; set; }