Improve Role Based Access Control Page in Guides Section

[fbryo21]

What is the improvement or update you wish to see?

The code must be explained more detail, in the Getting a role part.

The code:
return { role: profile.role ?? "user", ... }
(The ... part shows an error said "Expression Expected)

Is there any context that might help us understand?

Give more details explanation about Role Based Access Control, especially using with database (ex: MongoDb)

Does the docs page already exist? Please link to it.

https://authjs.dev/guides/role-based-access-control