Intro to Identity needs more information to function as a tutorial

### Description

UUF verbatim:

>I tried to follow this tutorial.1) The project setup stage is unclear2) The code discussed for _userManager is not generated anywhere.3) Probably other issues but I can't progress further at the moment

The article needs more information if it is to function as a tutorial, or explain that it is not a tutorial and the reader needs to be familiar with ASP.NET Core.

### Page URL

https://learn.microsoft.com/en-us/aspnet/core/security/authentication/identity?view=aspnetcore-8.0&tabs=visual-studio

### Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/security/authentication/identity.md

### Document ID

0e0d870e-e49a-e16c-c259-68d58e701b8f

### Article author

@Rick-Anderson