Add "Pis" to the list of validators

Author: henriquemoody

docs/VALIDATORS.md

@@ -192,6 +192,7 @@
   * [NotOptional](NotOptional.md)
   * [Pesel](Pesel.md)
   * [Phone](Phone.md)
+  * [Pis](Pis.md)
   * [Sf](Sf.md)
   * [Url](Url.md)
   * [Vatin](Vatin.md)
@@ -304,6 +305,7 @@
   * [Pesel](Pesel.md)
   * [Phone](Phone.md)
   * [PhpLabel](PhpLabel.md)
+  * [Pis](Pis.md)
   * [Positive](Positive.md)
   * [PostalCode](PostalCode.md)
   * [PrimeNumber](PrimeNumber.md)