Fixes #11764: Add meta data to docs for description, keywords, and authors

_includes/header.html

 <meta charset="utf-8">
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
-<meta name="description" content="">
-<meta name="author" content="">
+<meta name="description" content="Bootstrap, a sleek, intuitive, and powerful mobile first front-end framework for faster and easier web development.">
+<meta name="keywords" content="HTML, CSS, JS, JavaScript, framework, bootstrap, front-end, frontend, web development">
+<meta name="author" content="Mark Otto, Jacob Thornton, and Bootstrap contibutors">
 
 <title>
   {% if page.title == "Bootstrap" %}