Source:
I just found a sweet and short introduction on how to attach HTML to the current content!
add_filter('the_content', 'add_post_content');
Basically, you append the post content after your custom content, then return the result.
function theme_slug_filter_the_content( $content ) {
$custom_content = 'YOUR CONTENT GOES HERE'; $custom_content .= $content; return $custom_content;
}
add_filter( 'the_content', 'theme_slug_filter_the_content' );
Have fun! Cheers,