Add viewport meta to template.php

Find this function:

function my_theme_preprocess_html(&$variables)

and insert this code at the end. If the function does not exist, please, create it.

$viewport = array(
'#tag' => 'meta',
'#attributes' => array(
'name' => 'viewport',
'content' => 'width=device-width, initial-scale=1, maximum-scale=1',
),
);
drupal_add_html_head($viewport, 'viewport');
}