The following code placed in functions.php will add placeholder text to your gravity forms:
// Gravity Forms Placeholder Text -------------------------------
/* Add a custom field to the field editor (See editor screenshot) */
add_action("gform_field_standard_settings", "my_standard_settings", 10, 2);
function my_standard_settings($position, $form_id){
// Create settings on position 25 (right after Field Label)
if($position == 25){
?>