title: get url of site from which user click our link
body: <p>Any one knows how to know the site name from which user click our link.</p>
  
  <p>Like the ads company site, how they know from which site user opened their site.       </p>
  
  <p>Like we send the email to many users and when a user clicks on the link how can we know about the site name from which user click our link.</p>