add various meta tags

frontend/public/index.html

@@ -5,6 +5,24 @@
   <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
   <meta name="theme-color" content="#000000">
+
+  <!-- For search engines -->
+  <meta name="description" content="A tool to visualize decentralized social networks." />
+  <!-- Open Graph -->
+  <meta property="og:site_name" content="fediverse.space" />
+  <meta property="og:description" content="" />
+  <meta property="og:image" content="%PUBLIC_URL%/preview.png" />
+  <meta property="og:image:type" content="image/png" />
+  <meta property="og:image:width" content="914" />
+  <meta property="og:image:height" content="679" />
+  <meta property="og:image:alt" content="A screenshot of fediverse.space. Shows a graph of fediverse instances." />
+  <!-- Twitter cards -->
+  <meta name="twitter:card" content="summary_large_image">
+  <meta name="twitter:title" content="fediverse.space">
+  <meta name="twitter:description" content="A tool to visualize decentralized social networks.">
+  <meta name="twitter:image" content="%PUBLIC_URL%/preview.png">
+  <meta name="twitter:image:alt" content="A screenshot of fediverse.space. Shows a graph of fediverse instances." />
+
   <!--
       manifest.json provides metadata used when your web app is added to the
       homescreen on Android. See https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/
@@ -30,4 +48,4 @@
   <div id="root"></div>
 </body>
 
-</html>
+</html>