Clarified attribute mapping docs.

[dino8890]

PR related to the issue #334.

The current documentation makes it seem that attributes will be mapped to "profile" object if configured. In Django parlance, "profile" typically refers the model related to the User via OneToOneField.

Excerpt from Django docs:

If you wish to store information related to User, you can use a OneToOneField to a model containing the fields for additional information. This one-to-one model is often called a profile model, as it might store non-auth related information about a site user. For example you might create an Employee model:

This is not the case, and this changes makes it clear that attributes will be mapped to the User model only, including custom User models if configured.