Update TodoListController.cs
Update TodoListController.cs

added comment abut Context.User vs ClaimsPrincipal.Current
Azure-Samples/active-directory-dotnet-native-aspnet5,AzureADSamples/NativeClient-AspNet5,AzureADSamples/NativeClient-AspNet5,Azure-Samples/active-directory-dotnet-native-aspnet5