Update tmpl_editor.md

NB: Modificata solo la riga 28: "You build have all the template files you need (it is common to separate the different templates or templates parts in separate files to enhance readability), but at least one  template file named **index.twig** should exist, to make the application work correctly."
Merge pull request #12 from evecchietti/patch-9

Update tmpl_editor.md (attenzione, modificata solo la riga 28)