Provide Microsoft.AspNetCore.Identity.UI package README (#57580)

* Add PACKAGE.md

* Update src/Identity/UI/src/PACKAGE.md

Co-authored-by: Stephen Halter <halter73@gmail.com>

* Update src/Identity/UI/src/PACKAGE.md

Co-authored-by: Stephen Halter <halter73@gmail.com>

---------

Co-authored-by: Stephen Halter <halter73@gmail.com>

Author: MackinnonBuck

src/Identity/UI/src/PACKAGE.md

@@ -0,0 +1,43 @@
+## About
+
+`Microsoft.AspNetCore.Identity.UI` provides the default Razor Pages UI for the ASP.NET Core Identity framework.
+
+## Key Features
+
+* User registration and login functionality
+* Account management
+* Two-factor authentication
+
+## How to Use
+
+To use `Microsoft.AspNetCore.Identity.UI`, follow these steps:
+
+### Installation
+
+```sh
+dotnet add package Microsoft.AspNetCore.Identity.UI
+```
+
+### Configuration
+
+Add the following code to the `Program.cs` of your ASP.NET Core app:
+
+```csharp
+builder.Services.AddDefaultIdentity<IdentityUser>()
+    .AddEntityFrameworkStores<ApplicationDbContext>();
+
+var app = builder.Build();
+
+app.UseAuthentication();
+app.UseAuthorization();
+
+app.MapRazorPages();
+```
+
+## Additional Documentation
+
+For additional documentation and examples, refer to the [official ASP.NET Core Identity documentation](https://docs.microsoft.com/aspnet/core/security/authentication/identity).
+
+## Feedback & Contributing
+
+`Microsoft.AspNetCore.Identity.UI` is released as open-source under the [MIT license](https://licenses.nuget.org/MIT). Bug reports and contributions are welcome at [the GitHub repository](https://github.com/dotnet/aspnetcore).