how to add an attachment to a php contact form - php

Question

I have made a contact form that allows users to send me messages, but what I couldn't add is the ability for them to send me a file with it. Here is my code:
<form action="mail.php" method="post" enctype='multipart/form-data'>
<input type="text" class="feedback-input" id="firstname" name="firstname" placeholder="First Name" size="30" required="">
<br/>
<input type="text" class="feedback-input" id="lastname" name="lastname" placeholder="Last Name" size="30" required="">
<br/>
<input type="email" class="feedback-input" id="title" name="title" placeholder="E-mail" size="30" required="">
<br/>
<textarea name="message" class="feedback-input" placeholder="What can I help you with?" style="height: 150px;" required=""></textarea><br/>
<br/>
<input type="file" name="file" id="file" placeholder=" " tabindex="1" required/><br/>
<input type="submit" name="submit" id="Submit" value="Send">
and this is the mail.phph file:
<?php
$firstname = $_POST['firstname'];
$title = $_POST['title'];
$lastname = $_POST['lastname'];
$message = $_POST['message'];
$ip = $_SERVER['REMOTE_ADDR'];
$formcontent=" From: $firstname $lastname \n Email Address: $title \n IP: $ip \n\n Description : $message";
$recipient = "myemail#yahoo.com";
$subject = "New Message!!";
$mailheader = "From: $title \r\n";
mail($recipient, $subject, $formcontent, $mailheader) or die("Error!");
header("Location: www.mythankyoupage.com");
die();
?>