title: Detect viewport orientation, if orientation is Portrait display alert message advising user of instructions
body: <p>I am building a website specifically for mobile devices. There is one page in particular which is best viewed in landscape mode. </p>
  
  <p>Is there a way to detect if the user visiting that page is viewing it in Portrait mode and if so, display a message informing the user that the page is best viewed in landscape mode? If the user is already viewing it in landscape mode then no message will appear.</p>
  
  <p>So basically, I want the site to detect the viewport orientation, if orientation is <strong>Portrait</strong>, then display an alert message advising the user that this page is best viewed in <strong>Landscape</strong> mode.</p>