Add open graph tags and artwork for social media

src/includes/head.html

@@ -3,3 +3,23 @@
 <link rel="icon" href="/resources/images/favicon.png">
 <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Crimson+Text:400,800|Maven+Pro:400,700,900|Montserrat:400,700|PT+Mono&display=swap">
 <link rel="stylesheet" href="/resources/css/common.css">
+
+<!-- General metatags -->
+<meta name="author" content="Caddy 2">
+<meta name="description" content="Caddy 2 is a powerful, enterprise-ready, open source web server with automatic HTTPS written in Go">
+<meta name="theme-color" content="#5ea9a2">
+
+<!-- Open Graph tags -->
+<meta property="og:type" content="website" />
+<meta property="og:url" content="https://caddyserver.com/" />
+<meta property="og:title" content="Caddy 2 - The Ultimate Server with Automatic HTTPS" />
+<meta property="og:description" content="Caddy 2 is a powerful, enterprise-ready, open source web server with automatic HTTPS written in Go" />
+<meta property="og:image" content="https://caddyserver.com/resources/images/caddy-open-graph.jpg" />
+
+<!-- twitter card tags additive with the og: tags -->
+<meta name="twitter:card" content="summary_large_image">
+<meta name="twitter:domain" value="caddyserver.com" />
+<meta name="twitter:title" value="Caddy 2 - The Ultimate Server with Automatic HTTPS" />
+<meta name="twitter:description" value="Caddy 2 is a powerful, enterprise-ready, open source web server with automatic HTTPS written in Go" />
+<meta name="twitter:image" content="https://caddyserver.com/resources/images/caddy-open-graph.jpg" />
+<meta name="twitter:url" value="https://caddyserver.com/" />