How to add Google font

I tried to add Google font “Prociano” by adding this code in functions.php but the font is not appearing in the list.
add_filter( ‘avf_google_heading_font’, ‘avia_add_heading_font’);
function avia_add_heading_font($fonts)
{
$fonts[‘Prociono’] = ‘Prociono’;
return $fonts;
}

add_filter( ‘avf_google_content_font’, ‘avia_add_content_font’);
function avia_add_content_font($fonts)
{
$fonts[‘Prociono’] = ‘Prociono’;
return $fonts;
}