Fix .md syntax error in code block display

[michalczukm]

Now this code block displays as one line:

we need to define some users: ```csharp using Thinktecture.IdentityServer.Core.Services.InMemory;

static class Users { public static List Get() { return new List { new InMemoryUser { Username = "bob", Password = "secret", Subject = "1" }, new InMemoryUser { Username = "alice", Password = "secret", Subject = "2" } }; } } ```

I added missing enter.