Add to Readme thelimitation that Controllers that inherit from APIController wont have validation trigger automatically

[francis04j]

Validators are not triggered automatically for NET Projects that make use of ApiController attribute and conventions as described here.

This mean that if your controller does not inherit ControllerBase or other controller based classes that are provided out of the box, validators won't get triggered automatically

Issue here: #35 (comment)

Code culprit here: https://github.com/SharpGrip/FluentValidation.AutoValidation/blob/master/FluentValidation.AutoValidation.Mvc/src/Filters/FluentValidationAutoValidationActionFilter.cs

[mvdgun]

Hi @francis04j, could you check out #40? I think that solves your problem.