Added tests to the general help message.

src/dotnet/commands/dotnet-help/HelpCommand.cs

@@ -26,6 +26,7 @@ Common Commands:
   build         Builds a .NET project
   publish       Publishes a .NET project for deployment (including the runtime)
   run           Compiles and immediately executes a .NET project
+  test          Executes tests in a test project
   repl          Launch an interactive session (read, eval, print, loop)
   pack          Creates a NuGet package";
         public static readonly string ProductVersion = GetProductVersion();