Small explanation with two php blocks break

The two php blocks were too close together, as can be seen in the http://docs.phalconphp.com/en/latest/reference/validation.html documentation page. Note that this is not visible in github's Preview. With the added explanation, they are also separated, so double benefit from a simple edit.
Merge pull request #430 from FranciscoP/patch-1

Small explanation with two php blocks break