added the example Twig Code for the HTML5 no novalidate attribute

in the form documentation, there is a notice about the no validate HTML5 attribute, but without the twig example.

I added the twig code
Fix white spaces in the previous commit
Added the PHP no validate example

tested on symfony 2.3
added PHP file comment
added configuration block

I added no semicolon at the end of the PHP echo because in all other examples there exists no semicolon
[#3170] Tabbing out the code example so it's in the sidebar