How to add text as page variable to node add form? Or in other works print explanation/guideline text
The core page.tpl.php template doesn't know anything about any current node object or help information from its node type. The snippet you're using is for printing a region named help, not a node type's help test.

That help information is retrieved by the System help block and is placed in whatever theme region you've configured in the block admin UI (/admin/structure/block). You're better off utilizing that block with your theme regions rather inserting a variable into your page template. 

However, if you're really wanting to push this information into your template you can evoke node_help() to retrieve the information for your template variable and push in your template.php's template_preprocess_page() function:

/**
 * Override or insert variables into the page template.
 */
function MYTHEME_process_page(&amp;$vars) {
  // $help_text will be available as printable markup with page.tpl.php
  $vars['help_text'] = node_help(current_path(), arg());
}