Add Place Holder Text For WordPress Comment form Name Field.php

function modify_comment_form_fields($fields){
    $fields['author'] = '<p class="comment-form-author">' . '<label for="author">' . __( 'Name' ) . '</label> ' . ( $req ? '<span class="required">*</span>' : '' ) .
                    '<input id="author" name="author" type="text" placeholder="Real name, please, no keyword spamming!" value="' . esc_attr( $commenter['comment_author'] ) . '" size="20"' . $aria_req . ' /></p>';
    return $fields;
}

add_filter('comment_form_default_fields','modify_comment_form_fields');

Style Name Field Input Field.css

.comment-form-author input {
    background-color: #FFFFFF;
    border: 1px solid #DDDDDD;
    border-radius: 3px 3px 3px 3px;
    box-shadow: 1px 1px 3px #EEEEEE inset;
    color: #999999;
    font-size: 1.4rem;
    padding: 1.6rem;
    width: 100%;
}