Docs about `UserManager`

[gao-sun]

Summary

I couldn't find any documentation on UserManager, although it appears to be a crucial class for integration.

The sample code in the demo app is excellent for demonstrating the usage. Will it be better to include some documentation in the README.md? This would be very helpful for newbies like myself.

API Changes

N/A

Intended Use Case

For smoother integration.

[GeertvanHorrik]

I think it's a great idea, but am a "little" constrained in time.

@alexfdezsauco what do you think?

[alexfdezsauco]

That is a good idea. Will try to draft a section ASAP, including the required modifications of App.razor .