Update controllers.md with whitelist info

Add a hint section bellow the DTO description about the whitelist option from the ValidationPipe.

Author: luanpersini

content/controllers.md

@@ -407,6 +407,8 @@ async create(createCatDto) {
 }
 ```
 
+> info **Hint** Our `ValidationPipe` can filter out properties that should not be received by the method handler. In this case, we can whitelist the acceptable properties, and any property not included in the whitelist is automatically stripped from the resulting object. In the `CreateCatDto` example, our whitelist is the `name, age and breed` properties. Learn more [here.](https://docs.nestjs.com/techniques/validation#stripping-properties)
+
 #### Handling errors
 
 There's a separate chapter about handling errors (i.e., working with exceptions) [here](/exception-filters).