# Adds instruction text after the post title input
function emersonthis_edit_form_after_title() {
    $tip = '<strong>TIP:</strong> To create a single line break use SHIFT+RETURN. By default, RETURN creates a new paragraph.';
    echo '<p style="margin-bottom:0;">'.$tip.'</p>';
}
add_action(
    'edit_form_after_title',
    'emersonthis_edit_form_after_title'
);