Oleg0,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
$('#edit-comment').attr({'placeholder':'Введите тут комментарий'});
});
</script>
</head>
<body>
<textarea cols="60" rows="15" name="comment" id="edit-comment" class="form-textarea" ></textarea>
</body>
</html>