Add docs to show how to set user/role model.

docs/quickstart.rst.inc

@@ -97,6 +97,16 @@ the Role class to adapt your application, here is an example::
         def get_by_name(name):
             return Role.query.filter_by(name=name).first()
 
+After create role model, you can add your model to Flask-RBAC::
+
+    rbac.set_role_model(Role)
+
+Or use decorator to set role model for Flask-RBAC::
+
+    @rbac.as_role_model
+    class Role(RoleMixin):
+        # codes go here
+
 
 Set User Model
 --------------
@@ -143,6 +153,16 @@ Well, if your application works under SQLAlchemy::
             for role in self.roles:
                 yield role
 
+Same as role model, you should add user model to Flask-RBAC::
+
+    rbac.set_user_model(User)
+
+Or using decorator::
+
+    @rbac.as_user_model
+    class User(UserMixin):
+        # codes go here
+
 
 Set User Loader
 ---------------