Improve documentation for custom-header

// We support post thumbnails (now known as "featured images"). A post thumbnail is displayed

// in the header of a post.

// If there is no post thumbnail specified, we fall back to a default header image...

add_theme_support('post-thumbnails');

// - add support for header image

add_theme_support('custom-header', array('default-image'=>get_template_directory_uri().'/img/header.jpg', 'uploads'=>true));

// ...which can also be customized (site-wide)

add_theme_support('custom-header', array(

    'default-image' => get_template_directory_uri().'/img/header.jpg', 

    'uploads'       => true)

);

// - add support for custom menus

add_theme_support('menus');