Go to Settings > General Settings and under Meta tags heading, you can add meta tags. Please make sure to use proper formatting. Here're some examples of the the meta tags that are used:
<meta name="description" content="Free Web tutorials">
<meta name="keywords" content="HTML,CSS,XML,JavaScript">
<meta name="author" content="John Doe">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
