Add benchmark runner.

osu.Game.Benchmarks/Program.cs

@@ -1,13 +1,17 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using BenchmarkDotNet.Running;
+
 namespace osu.Game.Benchmarks
 {
     public static class Program
     {
         public static void Main(string[] args)
         {
-
+            BenchmarkSwitcher
+                .FromAssembly(typeof(Program).Assembly)
+                .Run(args);
         }
     }
 }