Added og-metadata to index page

- image and URL properties are only included if
 the server url is set, because opengraph
 protocol does not support relative links

Signed-off-by: Erik Michelson <erik@liltv.de>

public/views/index/head.ejs

@@ -6,6 +6,15 @@
 <meta name="mobile-web-app-capable" content="yes">
 <meta name="description" content="<%= __('Best way to write and share your knowledge in markdown.') %>">
 <meta name="keywords" content="Collaborative, Markdown, Notes">
+<meta property="og:title" content="CodiMD - <%= __('Collaborative markdown notes') %>">
+<meta property="og:description" content="<%= __('Best way to write and share your knowledge in markdown.') %>">
+<meta property="og:type" content="website">
+<% if (serverURL !== "") { %>
+<meta property="og:url" content="<%- serverURL %>">
+<meta property="og:image" content="<%- serverURL %>/favicon.png">
+<meta property="og:image:alt" content="CodiMD logo">
+<meta property="og:image:type" content="image/png">
+<% } %>
 <title>CodiMD - <%= __('Collaborative markdown notes') %></title>
 <link rel="icon" type="image/png" href="<%- serverURL %>/favicon.png">
 <link rel="apple-touch-icon" href="<%- serverURL %>/apple-touch-icon.png">