Add favicon, social card and link preview metadata

The page had no favicon and no og:image, so a shared link rendered as bare
text. Adds the brand mark as the icon and apple-touch icon, the launch card as
the social image, and the Open Graph and Twitter tags to go with it.

Author: oxpull

assets/django-ox-ad-1200x630.png

@@ -5,8 +5,25 @@
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <title>Oxpull Pro waitlist. A production worker for Django Tasks</title>
   <meta name="description" content="A database-backed worker for Django's Tasks framework. Transactional enqueue, no broker. Join the waitlist for the Pro tier.">
+  <link rel="canonical" href="https://oxpull.github.io/">
+
+  <meta property="og:type" content="website">
+  <meta property="og:site_name" content="Oxpull">
+  <meta property="og:title" content="A production worker for Django Tasks">
+  <meta property="og:description" content="A database-backed worker for Django's Tasks framework. Transactional enqueue, no broker. Join the waitlist for the Pro tier.">
+  <meta property="og:url" content="https://oxpull.github.io/">
+  <meta property="og:image" content="https://oxpull.github.io/assets/social-card.png">
+  <meta property="og:image:width" content="1200">
+  <meta property="og:image:height" content="630">
+  <meta property="og:image:alt" content="django-ox: Django 6 shipped Tasks, the production worker is missing.">
+  <meta name="twitter:card" content="summary_large_image">
+  <meta name="twitter:title" content="A production worker for Django Tasks">
+  <meta name="twitter:description" content="A database-backed worker for Django's Tasks framework. Transactional enqueue, no broker. Join the waitlist for the Pro tier.">
+  <meta name="twitter:image" content="https://oxpull.github.io/assets/social-card.png">
+
   <link rel="stylesheet" href="style.css">
-  <link rel="icon" href="data:,">
+  <link rel="icon" href="assets/favicon.png">
+  <link rel="apple-touch-icon" href="assets/favicon.png">
 </head>
 <body>
   <div class="wrap">

assets/favicon.png

@@ -6,7 +6,8 @@
   <title>You're on the list. Oxpull Pro</title>
   <meta name="robots" content="noindex">
   <link rel="stylesheet" href="style.css">
-  <link rel="icon" href="data:,">
+  <link rel="icon" href="assets/favicon.png">
+  <link rel="apple-touch-icon" href="assets/favicon.png">
 </head>
 <body>
   <div class="wrap">